I know my site highlighted a lot of bugs in Netscape 6 and Mozilla when I tried it through them. A lot of these have been resolved now though. Perhaps you should report it as a bug to the Opera team.

It is important to get these little browsers up and running as best as possible and they need all the info/feedback they can get. Sometime in the next three weeks I shall be endeavouring to make megalithomania 100% WC3 compliant.

Can't shed any light on this particular issue (the file upload thang), but regarding Opera in general... it has great XHTML / CSS support, but a really lousy handling of the Document Object Model (for this reason, any half-complex JScript / VBScript may give Opera some problems).

As i say; no idea why that would be putting the kibosh on file uploads (it usually just chokes when you do things like putting little JScript controls in the page to show/hide sections of text). But something to consider perhaps.