Many good comments already, though I´d have a different interpretation on some. Anyway, here´s my view of your queries:
QUOTE (Nimblegrund @ Oct 19 2009, 08:59 AM)

I have long been a fan of the setting for Shadowrun. I have had a number of SR sourcebooks over the years, but I have only actually played shadowrun a couple times. Now that I have the new 4th edition book, I think sometime in the future I would like to run a SR game, but there are a few things I am not clear on. I might come up with more questions later, and if I do I will put them here.
1. I understand that the megacorps are kind of like countries in their own right... and a person can be a citizen of a megacorp. But how does someone actually become a citizen of a megacorp? Where do you have to be born? It's not like Ares Technology is a place on the map. What if you get fired? Do you lose your citizenship?
Extraterritorial Enteties like the bigger megacorps have the right to give out SINs of their own, just like countries and it´s thair decision on what basis the give them out and retract them again. How they deal with it, however, depends on the corps philosophy and the employee in question. MCT i.e. is known for a very elaborate corp-culture and many of their employees are probably MCT citizens, as would their kids, which are educated in MCT Schools, live in MCT enclaves and will become MCT employees in most cases, anyway. Other corps might not give citizenship at all, or only to a select few. Ares as 'the american megacorp' i.e., might make a point out of employing UCAS citizens, and thus not give a corp-SIN to everyone. Most corps will probably retract citizenship upon contract-termination, which could leave a fired wageslave not only unemployed, but also SINless (unless they can get a SIN from someone else) - all the more incentive to work hard and play nice with mother corp, especially, when all your savings are in corp-script!
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2. Why would anyone ever want their cyberlimbs to be wirelessly active? or their cybereyes? I kind of understand that it would be fun for the player to hack into some big bruiser's cyberarm and have him shoot himself. But wouldn't it be profoundly stupid to have your ARM be connected to the matrix? The explaination in the book doesn't sit right with me.
Because people ARE stupid. most runners will either slave their implants to some very secure core node (usually the com) or have it offline, alltogether (you can still move your cyberlimb with the integrated direct neural interface, you can´t just use all the convenient wifi features). corp sec will probably asked, to follow certain security protocols, but it´s like people in the real world, connecting their work-pcs tot he internet (or certain sides), even when it´s not permitted, or like people leaving valuables liing arround at their desk. Some do, some don´t. Professionals are less likely to be lax about it, though.
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3. My brother would like to play a Technomancer rigger. How would this work? Are technomancer riggers at a disadvantage over the usual type of rigger?
Unwirred has a few new tricks for rigging TMs, otherwise I don´t know what´s really better.
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4. Suppose I am setting up a run for my players. It is your typical get in/get out mission. What sort of challenges would I need to prepare for a hacker? I understand the goals: turn off the cameras, open the doors, turn off the sentries, get the data, etc. How do I know what sort of security measures to throw at the hacker?
Breaking it down into small tasks and short subsystem hacks is probably a good idea. but oldschool remote hacker backup still works in some places. depends on how interconnected the facilities systems are.
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5. This sort of figures into #4, but I recall previous editions descriptions of decking and I remember seeng maps of squares, diamonds and circles connected by lines serving as maps for decking and showing where nodes go and what they do etc. but this time around their description of nodes is very broad and the maps are gone. I feel like there was something I could have taken away from that.
Thing of the past. If you have complex webs of nodes and devices, however, it might be a good idea to do some kind of map, instead of just writing down the subscription lists.
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6. This one I suspect I may get lambasted for, but... I don't like the idea of one player getting multiple turns while another doesn't. I remember from previous editions that all one would have to do to get a second turn would be to roll above 10 on initiative. I don't think that is true anymore, but I see that there are spells and cyberware that can give people more actions. Suppose I reduced any and all additional turns to a single (and I don't have my SR book with me right now, so I will borrow a term from D&D) "standard" action. would this break the system?
difficult, as others noted. In any case you´d either have to houserule all reflexincreasing stuff to i.e. give a bigger bonus to reaction and/or initiative, to make it worthwhile, or leave it out of the game all together. just considdering this for balance reasons, I´d not change it. the ware is comparatively cheap for the lower levels and there´s also a lot of drugs, that can be used in an emergancy. But I agree that it is a key-mechanism for many fighting-types, flavour and usefullness wise.
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7. How do you interface with your commlink? One page describes a character who controls his commlink with a scroll wheel. I cannot possibly imagine surfing the internet with only a scroll wheel. How do they see the information they recieve? I noticed it mentions that commlinks can make holograms. So if someone is walking down the street surfing the matrix, is a glowing window floating in front of him? Is he wearing special shades? moving his commlink around like a mouse? How does he type? This is all presuming that he has nothing implanted in his head.
You can just use it like a cellphone nowerdays, with a bunch of kays and a tiny display screen. a fullsize, felexible, rollout keyboard can be used for regular typing. I think the mousewheel example is probably not meant to be a single wheel controll, but part of an ensamble, however, a wheel and a few keys can go a long way (think i-pod). others may have built in holoproyectors however, but the most common is probably some imagelink (in glasses, contacts, monocle, goggles or implanted, making all these cool 3d AR elements visible) headphones (or implanted audiolink) and AR gloves (allowing you to use AR controlls, by 'touching' the icons) unless you go trodes/sim or full cyber dni. The general idea is that there is no real default, however and everyone just uses, what he likes best, from the tiny joystick at the belt, to the datajack thought controll.