I've had the Ipad 3 since day 1--64 GB, 3G (and wooee, this week we got Lte/4G though I use very little data--usually less than 50% of my 1GB). Whenever I turn on cellular data, since I don't leave it on all the time--but even if it is still on, when switching from wifi to 3G which actually happens quite often I almost always have to reboot. I know this seems to be a known issue.
The second one may be related. I have two email accounts, a Charter one and a Gmail one. A number of times a day I get a message saying the gmail can't be gotten. I have to reboot then to download Gmail--and its a pain. Does not happen with Charter mail but most of mine is gmail. It didn't happen with Ipad 1 but not sure if this happened after IOS 5.1, Ipad 3--don't think it is firmware related as my Ipad 1, used just for music now, still doesn't appear to have the problem. Curious if others have the Gmail/reboot issue.