I think I've been away too long I've forgotten everything I loved about Opera. Most of the plugins I wanted are built in. Only things missing are:
Plugin for Delicious (but I'm trying out Opera Link)
FireFTP (I can live without that and just open Firefox)
ScreenGrab! to save a JPEG of a web page.
And Gmail and Reader notifier.
Hmmmm you can kinda work your way around these i guess.
I use Delicious, i have a button that javascript sends the current link i'm at to delicious, and i've set up a custom search under "d" to search bookmarks there, which covers all my delicious needs.
Opera sucks at FTP, for something that likes to call itself jack of all trades (newsgroups, irc, bittorrent etc...) i'll never understood why they didnt go a little further with the FTP implementation.
I guess screengrab is clever and makes everything out of view on a website a jpg? I have no idea how to do this with opera (i've never needed to personally). I do seem to remember i fell across a website that does this though so a simple javascript button could do the same thing, tried googling to find a suitable website but failed so far.
I keep track of Gmail and facebook and all manner of other things with Digsby (and its also my IM of choice as well). The only thing it doesn't do right now is Google Reader, but they've spoke about adding that and IRC and all manner of things too, so i guess i can only wait.
So with this long post and generally not much help, thats generally what i do whilst using Opera, it would seem a lot of that is a work around rather than a solution though i tend to agree!