First of all, I don't mean to close my eyes on the problems that some people have after upgrading to 5.1. I'm just gonna tell my side of story doing it. A lot of people complain bout the new 5.1, but I've been googling bout it and I found that there're also people who's happy with it. And I tell you, I'm that happy one.
I did quite a long jump to 5.1 from 4.3.1 on my ipad 1. I did the backup first, upgrade and restore. Been sometimes since I did that, and not a thing is wrong with my ipad. In fact, it gets smoother as I feel it. I used to deal with crashes with my previous 4.3.1, especially when dealing with new apps. I could hardly play infinity blade and batman arkham city lockdown back then. Had to restart everytime I want to play it. RAM problem they say, and I agree with that.
But after upgrading to 5.1, everything works smooth as silk. Infinity blade II, Batman arkham city, you name it. No more crashes. Safari works fine, wifi works fine, and pretty much everything else is fine. Well maybe I got lucky.
I'm writing this just to tell you guys not to worry about upgrading. Chance of failure...you bet it happens. And guess what, I'm not the only one winning the bet.