I would like to let a particular usergroup upload more than 10 pics at a time. If I manually edit num_file_upload in the usergroups table I can get a number greater than 10. Should this work properly? Could I run into any trouble doing this?
depends on the file size you allow. Having a larger number of pics uploaded at once may result in timeouts and/or performance issues on your webserver, as CPU load will go up. There's no general recommendation on this matter, as it greatly depends on server setup. The max of 10 files at once was just a number we came up with (we figured it should be save for most users). If it works for you with a higher number, then fine. If you (or your users) experience problems (or "strange behaviour"), go back to the original limit of 10.
Joachim