Happy 10th anniversary to you Opera, and thank you for the free registration codes! (Free registration codes are available until midnight CET (GMT +1) on Wednesday 31st of August.)
For several years (about 4 to 5, I think) I was a happy Opera user but when I couldn’t use it for work (I needed the jar:* support in Firefox/Netscape/Mozilla) I eventually switched as juggling multiple browsers around is a pain in the long run.
However, running Opera last night and again this morning, I’m reminded of several of its strong points:
- Low memory footprint (particularly useful on the 96MB/300MHz Pentium laptop).
- Built-in support for:
- Mouse-gestures
- Customizing tab-order
- Session saving
- Better support for resizing, it resizes images as well, not just fonts like Firefox.
- The fact that I can place the tab-bar on the left (or right), not just the top or bottom of the window.
When are you going to add XUL/jar support, Opera? 
Update: I can’t believe I never noticed the typo in the title (congralations instead of congratulations). Now fixed.
I never really got myself to use Opera long enough to get used to it (Symbian/S60 platform not withstanding), but I flip to it semi-regularly as an alternate renderer (either for testing or because some website is broken).