Works fine ............... EXCEPT, if you're inclined to update any iPad 1, I wouldn't recommend it.
Do some checking, because various forums are replete with issues, but 5.1 and iPad 1 do not make for a happy combination, with the principal complaint (and I experience this as well) ............. being repeated crashes of Safari (and, most likely, any browser). Having just ordered 3, I guess I won't soon have to deal with this, but it really is a problem for many. In my case, it's been reasonably tolerable in that I've been experiencing intermittent crashes, but there are many just can no longer connect to the Internet with any reliability or stability. I have friends who have experiences these same issues as well, so I know for a fact that it's not just me. So, at least in the case of iPad 1, I wish I had left well enough alone and would not recommend this upgrade.