Tip: if you want to solicit suggestions on forums, don't do it with a link to another place. Users likely won't bother to go sign up elsewhere just to answer your survey question.
The main thing I'd like to see is the browser actually work reliably. I have tried it in the various v4 betas, and then the v4 final release, and the network connection failures made it unusable. Setting the APN doesn't make any difference. Load a page, maybe it works. It refresh, it fails. Refresh a few more times and eventually it loads. Then hit refresh again and it fails again. Success to fail ratio for virtually every website tried was on the order of 80% fail/20% success. In the end, I gave up and have simply removed Opera Mini from my 8320.
If you do get it working, then the thing that would be most useful for me is the ability to download within Opera Mini, rather than having to fork out to the native Blackberry browser.