I have an iPad 1st Gen and it is slow, gets the 'grey screen of death' and frequently crashes with the free Life on Earth book. Have to keep quitting the App to get out of the grey screen of death, when it locks up just after the movie is loaded.
My first-generation iPad crashes out of apps very frequently (especially Safari and games). I was thinking that it must be a RAM issue, since iPad 1 only has 256 MB of ram, but there's a huge thread on the Apple support forums of people experiencing a similar issue (frequent app crashes, esp. Safari) that seems to be occurring with both the iPad 1 and iPad 2 since the latest update.
Some people have run diagnostic software to check RAM usage and that doesn't seem to be the problem in the majority of cases. Others have reported that it seems to have something to do with Java errors, and others have said a full restore could fix the issue. I wish Apple would address this, it's becoming very frustrating when Safari crashes about five times a day!