No major problems as long as you don't implement a feature new with FileMaker 11 and expect it to work from FileMaker 10.
After upgrading to FMPA 11 I've made so many design changes that I've actually set things so my solutions won't run on any version less than 11. I know some would say that's not wise, but there are so many differences (merge variables for example) that don't work on previous versions, but are so useful, that I feel it's a worthwhile gambit. Besides, I'm not a pro developer. I run my business using my solution and anyone who works for/with me will have access to FMP 11 so it's not a big deal. I recommend FMP 11 without reservation.
Phil: I'm going to have to do some more searching in FM11 to see if there's any new features that I might use that's not in FM10, but my database is really not that complicated in scripting or things like that. It's only complicated for me in the number of reports that I'm setting up plus having it run in basically a Kiosk mode so that the user does not have access to file menus. My target users are relatively unsophisticated computer users and so I'm trying to make it so that they won't even know that FM is the underlying software. Thanks.
David: I hadn't thought of looking at Wikipedia. I did find a similar table in the Knowledge Base, though. Thanks.
Rick: I hate to admit it, but I don't even know what a merge variable is! My solution does no calculations, only recording and documenting essentially text entries and then displaying them in various report formats to track inspection activities. Thanks.
However with all the glowing reports of FM11, I think I will just get the new version and use that.
Again, thanks for all the thoughtful replies.