There's currently a 131 page thread about the 3.1 lockups on Apple's own discussion forums, so I would say that it's affecting more than a "few". I realize that this is well under 1% of all iPhone users worldwide, but it's still a fair number of people. Why this isn't bigger news is beyond me.
Anyway, you can always roll back to 3.0.1 if you experience problems. It's a little bit of a PITA, but it's not TOO bad. Several have already posted links to rollback instructions, so I won't do that. Oh, and 3G is easier to rollback, but I think someone might have found a way to rollback the 3GS - not sure. I have the 3G and rolled back after the lockups. 1 app that I barely use released a newer version that only works with 3.1. It's a good thing my TimeMachine backup has all my older apps & files