Low memory crashes are a problem for a lot of folks, especially with the ipad1. I've been getting them a lot on my iapd 2 also. Have done everything including a complete wipe and setup from scratch - one app at a time. For me its just the web browsers and a couple of games. Looking at the Diagnostics and Usage you will see a lot of low memory issues. There are a bunch of long threads over on apple discussions. No acknowledgement from Apple (of course). It is really making my iPad pretty unusable.
OP, I did have some luck for a while turning off Spotlight Search helpers. It stopped my crashes for 3 weeks or so but they are back.
Since the issue for everyone who has posted started with IOS 5 I'm not convinced that exchanging it will help. For some reason its either not releasing memory correctly or there is a leak. Since not everybody is having the issue there has to be some sort of combination of actions that is causing it.
Plus I don't want another one (probably a referb) and I have $60 or so sunk into a screen protector and skin. At least I have an iPad 2. Folks with an iPad 1 are SOL I guess.
It's a shame because I do like my iPad, at least I used to when I could use it without all the crashes.