Hello,
I'm thinking of organizing a game for a few friends, and I've never played Shadowrun so far (despite the subscription date to this forum).
I'm reading now the first season of Shadowrun Missions, the scenario are nice. I was wondering if anyone cared to share tips on converting these 3rd ed. scenarios to 4th edition. Not much seems incredibly different, except maybe wifi, but maybe there are unforeseen differences further along the road.

Thanks to everyone who cares to comment.

Mostly, I eyeball it, when I convert adventures from older editions.
Important NPCs get a workover in Chummer, mooks just get a short look. Usually I go for 1:1 attributes while taking Intelligence and converting it to Intuition. Logic generally isn't necessary too much. Just enter the new gear values and you'll be fine.
When you convert high target numbers (say, 10, to notice something) change the number of hits needed and / or reduce the character's dicepool.

Thanks for the comment, the stat blocks are the least of my concern, I will give them a look in due time. I'm more worried about things settings-wise, i.e. some situations where having to find a cabled matrix connection is crucial to the adventure, something that would be completely off in a setting where wi-fi is ubiquitous. Just an example to show something I'm already looking out for - is there anything elese I should think about?

I think the Shadowrun 2050 book will be of help for you in this. I've not done an extensive read of this book, but it does look like there's a lot that'll be able to help you convert the SR3 missions into an SR4 format.