For me, it's mouse gestures. Last time I tried getting them in FF with a plugin, it just wasn't as well done (forces you to make distinctions between tabs and windows, for example, that you aren't used to having to think about). Mouse gestures get to be very addictive, and they really are a faster and better way to work.

I'm also a big fan of the developer tools. While similar to Firebug etc, I prefer some of the minor differences in Opera.

I also think built-in support for torrent files is a really nice feature (don't know if any other browsers have caught up with this yet).

Besides mouse gestures I've gotten so used to browsing via keyboard (especially when using Shift+arrow keys) that switching to another browser is nigh impossible, because I get irritated too easily.

And the builtin RSS reader is better than anything else I've come across (not that I spent that much time looking ;-))

I love the rss feed: no signing in, no opening tab upon tab upon tab, no silly magazine layout. Just the feed menu on the top of the page, the individual feeds displayed on the bottom- it's perfect.

It's always had great speed, performance, security and has a long history of innovation. When you consider how many features they've created that have become defaults across browsers, everyone is using Opera to one degree or another.

Chrome is a glorified data mining device and just feels overly sterile and corporate, FF grew complacent and has always been buggy, but Opera has everything I need built right into it:torrent client, note taker (very easy to use, super useful since I'l always taking notes on one tutorial or another), selective ad-blocking, the adress field doubles as a search field for any engine I want,it has the most customizable GUI and Opera Unite is awesome for file sharing- a couple friends and I use it to raid each others media collections every few months.

My reason number #322: Instant fully RAM-cached Back button.

I can't stand when other browsers sometimes reload pages when I go back/forward, especially when I had text typed in forms.

I see Opera as being flexible like FF but has the speed and UI polish of Chrome. That way, I only need to use one browser.

Top feature that no other browser offers: fully customizable UI. Right click on any UI element of the browser and select Customize->Appearance. The Toolbars and Buttons tabs allow full control over the browser UI so I can move buttons and toolbars to my heart's content.

Fully customizable keyboard navigation. Customizable using the interface at Settings->Preferences->Advanced->Shortcuts->Keyboard setup->Edit. Make sure to check the "Enable Single Key Shortcuts" option on the "Keyboard setup" pane to get the most out of it. Check out http://www.opera.com/browser/tutorials/nomouse/

Fast history navigation: This one isnt actually enabled by default; set the following preference to 3 opera:config#UserPrefs|HistoryNavigationMode The history is fully cached so there is absolutely no delay between pressing the back button and viewing the previous page in history and it comes up exactly at the point you left it.

Among other, smaller things - it's fast. And by fast I mean: it doesn't use 50-100% of processor. In Chrome, opening more than 2 tabs was a nigthmare. Same with Firefox.

I use it because

1) it is available on all the platforms I use (Linux, Maemo, Mac, Windows, Symbian) and syncs bookmarks to and fro

2) it can be secretly installed in my home on my work computer which runs a heavily customized old Debian without modern libraries.

* Really flexible UI and hotkeys - totally customizable

* A lot of the features I care about have native support, meaning they look and perform better (visual tabs, mouse gestures, ad blocking, etc.)

* Great performance

* I think Opera is probably more innovative than anyone else in the space - many of the new features that have shown up in other browsers recently are copied from Opera. I've had speed dial for ages.

* On Windows, at least, I think it looks a lot nicer than any of the other browsers. Though I guess FF4 copied it a bit so maybe that advantage is less now.

I use Opera mostly because I feel like it (yes, I know, poor reason), but generally Opera users like it because it's friendly to power users out of the box. It has a ton of UI features that don't appeal to many people, but that are loved by the people that do use them (e.g. search engine shortcuts, gestures, tab previews, etc).

Well instead of using two browsers (Fx and Chrome), mail/rss/chat client, a (very simple) torrent client and a note tracker (and some other software), you can simply use the unified package - Opera.

Firefox is dead slow if you add all the needed functionality build in Opera and Chrome doesn't have much going for it (speed-wise check the benchmarks; and Opera is very responsive when I keep my 50+ tabs open, whereas Chrome cannot handle the load, freezes the computer and uses a huge amount of memory).

Oh, by the way, the Opera default is "restore previous session" and it does not close all your tabs when you close the browser so you are encouraged to have one continuous browsing experience; I've been keeping some tabs open for years.

Just a sneak peek.

Reminds me of an old JWZ's quote: "Every program attempts to expand until it can read mail. Those programs which cannot so expand are replaced by ones which can."

I think all Opera's extra goodies are good only if you expect 75% of functionalities. E.g. Opera Chat still don't support encoding fallback (X-chat, IRSSI, mIRC, etc. does), or it is not very obvious to disable the built-in BitTorrent client (disable it in `about:config` by yourself), Opera Link that only merge two bookmarks together, requiring me to manually delete all default bookmarks before (or after) syncing, etc.

But it is a really good browser: fast, has minimum resource usage. I wish there is Opera Lite. (And hope Opera team to finally fix Asian language support.)

I agree, if you go for dedicated clients (irc, mail, rss) you will get more power/functionality if you need them; but I feel that in Opera I get the optimal balance between functionality and complexity. To each his own.

Still, I don't understand what benefits are to explicitly disabling Opera's built-in torrent client; why not use something else?

Opera always override default torrent application on my machine. I found it to be easier to just disable Opera's built-in BitTorrent than changing back the default every few days. I wish they have this simple "Use Opera to handle BitTorrent" checkbox in the Preferences.