I love Opera as well, and used it long before I even heard of Firefox. I use its email client as well, and though it could be improved on it is very easy and powerful in use (its filters are great!)
What I especially like in Opera:
* The speed! And the neat pop up progress bar (you have to enable this) where you can see the speed at which the site loads, how much more it has to load, how many more images, etc. If the images take too long to load, just switch the images off for this page with one click.
* The 'forward' and 'rewind' button. If you have a password saved with the 'wand', it enters it automatically when you press forward. Great also for browsing pictures: just click forward and you go to the next one (for most sites).
* Right - Left mouse click brings you back in history; left-right goes forward (or same as the forward button). It makes browsing so much easier! Very frustrating if you're using another browser that doesn't have this feature, and you're used to it.
* you can choose how to start Opera: load homepage, no pages, sessions (!), or just what was last opened.
* the trashcan (in the upper right corner): any tabs you have closed (including its history) can be easily opened again. If you just want the last closed tab, type Ctrl+Alt+Z and you are back there.
* The 'duplicate tab' option (right click on a tab). Again the history and all is duplicated.
* Site preferences. Have a site that doesn't recognises only IE? Edit your site preferences, and make Opera identify as IE, or even mask as IE.
* Press spacebar to go down the page (standard, no?). When you reach the end of the page, press spacebar again and it takes you to the next. Great for Google searches!
* Disable gif animation!
* Block unwanted ads.
* Asign shortcuts or nicknames to bookmarked sites
* The transfer (download) system. See how fast things go, where you are downloading from and where to, option to retransfer or pause transfer, or use the quick download option (just enter a url). Torrents will also appear there.
* the option to save particular file types (mp3, pdf, etc) to particular locations on your hard drive
* 'Work offline' option
* 'Links' panel: see where the site you are on links to.
* The notes feature. Just select some text, right click and select 'save to note'. A new note is created and the url is automatically preserved. Just double click on the note and the webpage is opened.
* the built in search engines. Type 'g ubuntu' and you do a google search for Ubuntu; z for amazon, etc.
* 'Fit to width': is the image to big and do you have to use the horizontal scrollbar, or is the page just badly designed for your small screen? Click the fit to width button and it is automatically resized or adjusted.
* Zoom easily in and out.
* Its easy to customise the look. Move all buttons around until you like where they are.
* etc.
Bookmarks