I'm pretty certain I've seen something about this, but now I cannot find it. So:

If I create a character with, for instance, Magic 5 and no implants, and later, in-game, want to put in some cyber, what happens? Lets say I take one Essence worth of 'wares, decreasing his Magic to 4 in the process. Then, I want to increase his Magic to 5 again. Do I have to pay 25 Karma to increase it to 5, or 30 Karma to increase it to an effective 6?

There is no "virtual maximum magic" or something like that.

Whenever you lose essence to get under a whole number, you lose a point of magic. You can raise magic to a maximum of essence + initiation grade. You pay the new rating*5 karma.

So in your example: you install cyberware... your magic falls to 4. You pay 25 karma to get it to 5.

You could also FIRST pay 30 karma to raise it to 6, and then install the one point cyberware and it will go down to 5. (But yeah: first install the cyberware and THEN raise magic back is way cheaper)

Thanks. In other words, unlimited potential for abuses!

Only if:

A) You start heavy cyber and a latent mage
B) Your GM is dumb enough to let you break the rules and buy cyber first
C) You play the Long Game and rack up bits of both as you go*

*And its not overpowered, because if you stuck to one route you'd be so much better.

Not really. Every point of Magic lost to 'ware also lowers your maximum Magic. And honestly, after 1-3 points of 'ware, it starts getting to a point of diminishing returns for awakened characters.

I can't imagine spending more than 2 essence on stuff for an awakened character. Except maybe an adept who is grabbing synaptic boosters 3 and muscle toner 4.

Usually it is 1 or 2 points, for me. 3 points is the extreme range, for a handful of concepts.

One of my players has latent awakening, I think we got to 1.8 points with .2 undecided.

He's got Synaptics 1, ceramic bonelacing (at half essence, which made it statistically better than the bone density increase he was looking at) and some other bits and pieces. For someone going latent awakened adept, I don't see improved reflexes as a real option, it takes too long to get to the pay off.

I really can't see any build including the very suboptimal latent awekening as abusive.

If Latent Awakening allowed the player to pick the magic related quality they ended up with then you could make some nice adepts that way. Going down to 1.x essence and then becoming a full magician would likely suck though.

I can see one, and that would be a hacker going for a latent awakening into an adept or mystic adept. That way they get to start with all their great hacker ware and everything, and then once they awaken they can just focus on raising magic and grabbing Improved Ability for hacking, cybercombat, computer, and whatever else they want.

You'd basically get the best of both the adept hacker and the mundane hacker. I don't know that it would be super abusive, but it would be potentially quite powerful.

But, as always, countered by the fact that latent awakening is only triggered by GM fiat.

True, but that's why you just save up a bunch of karma while you wait.

Well, arguably you can "save" BPs by buying low magic (3 or so) at chargen, lowering it back down to 1, and then paying less to get it back up. However... I don't know. Until you've accumulated enough karma to raise it to values that actually matter, you will just be static, while others are advancing. While it's cost-effective, it's probably much better from a gameplay perspective to just request the Power-point for initiation rule, or just limiting yourself to one point of ware.

Not to mention that stats over 4 are more cost efficient as BP than as karma.
(Cost of magic 5 as bp from magic 4: 10. Cost of magic 5 from 4 as karma: 25*)

*2 karma is "equal" to 1 BP.

Just one of many, many reasons to use Karmagen