I noticed something interesting to my opera browser:

I open an instance, and I open two tabs: hotmail, and a yahoo.

When I am checking opera in TM, I see ~ 350 MB at opera process.
When I check all ports opened by opera with CurrPorts (from http://www.nirsoft.net/) I see a lots of active connections. Ok.

I close all tabs. Opera browser remain opened in speed dial. Ok.

After few minutes, ~ 2-3, I see whole connection eaten by opera as closed (in CurrPorts). Ok.
But the RAM eaten is still ~300 MB, 280 MB ... for more than 40 minutes ... which is not happen at Chrome, or IE. Of course. after a while, Opera release RAM, and step down to 80MB, which is ok ... but why Opera browser doesn't release RAM right after all connection is closed ?