what is the "~/.local" and can I delete it?

/home/user/.local is kinda big (~5.6Gb on debian squeeze and 3.7 on ubuntu 12.04) for me, so, can I delete it?

~/.local – or more precisely, ~/.local/share – is where XDG-compliant programs store user data (e.g., fonts, mail messages) according to the XDG Base Directory specification.

The ~/.local folder also contains share/Trash, which is your trash bin. Everything you put in there of course takes up space. I assume this is the most likely cause of disk usage.

Check how much space it takes up with:

du -hs ~/.local/share/Trash

If you don't need to keep items in the trash, empty it through your file manager or just delete everything in share/Trash with:

rm -rf ~/.local/share/Trash

It's the new location for user-specific, application-specific data. Removing it will not affect the system as a whole, but it will erase a large amount of user data.