Hi,
So I have recently reported, that I had my iPad being reset at the apple store, but didn't restore from the backup. So far it was working smooth again... I then wanted to see what happens, after restoring my backup. First, it seemed to work quite fast as well (maybe a bit slower than I remember from iOS4). But after using it normally for a couple of days, it went back to being super slow again (crashes, keyboard and typing lags, etc).
So my last thing to try is reset and set up as new iPad (without restore). I hope this will help, even though I must say this is far from what I'm used to from apple. First it will take me loads of time to "manually backup" all app settings (i.e. bring them to paper) and also to bring them back on after having to install all apps again.
If that doesn't help I will ask apple to replace the device. Since I was the first in my local Apple Store to show up with that problem, I suppose there must be iPads 1 that work normally with iOS5? Maybe it's just the pads from a specific series of production...
Even though they were very friendly and helpful in the apple store, I am still very disappointed in Apple. In my Opinion you can't release a software for a device on which it won't work properly, at least not without giving the option to downgrade again. On my old PC laptop I do have the option to go back to Windows 98 if I wanted to...