I played around a lot with installing WINE and some stuff for party poker. Also I was following some tutorials on installing adobeair on x64 system. I believe I have downloaded quite a lot -> 200MB stuff which I will not ever use, are there some tools that will help me to erase anything that is incompatible with my system? For example I did not notice that I am downloading stuff for ubuntu 9, even though I have ubuntu 11 etc.
Start synaptic and install gtkorphan. Select System-->Administration-->Remove Orphaned packages, this will run gtkorphan. Ensure the Orphaned packages tab is selected and you'll see a list of orphaned libraries. Go down the list, ticking the checkboxes as you go: when you've ticked the lot, click on Ok and the prog goes to work. On completion, don't be surprised if the list fills again; just keep at it until finally there are no more orphans presented.
Then click Options and check the top box, 'Show orphaned packages with orphaned configuration files' and go through the same routine as previously described. This gets rid of the config files too, which is a Good Thing.
Ubuntu Tweak has a very useful Janitor function which also ferrets out 'surplus' files and deletes them; the Ubuntu Tweak web site has good install instructions (you have to add a ppa to your repositories)
Also, and closer to home, you have the option of opening a terminal and entering 'sudo apt-get autoclean'and hitting the return key to remove packages on your machine which are no longer installed.
Installing bleachbit and running it sudo is another great way to clean away unwanted stuff. So far, I've had no problems with it.
You'll be surprised how much more sprightly your machine is after a good spring clean...