I have upgraded to Ubuntu 13.04 a few days ago.
Last night I went to a friend's house where we were 5 persons total. Everyone noticed that the internet was slow - except me. For me it was fast.
So we decided to to a little experiment.We started turning off the laptops to see which was causing the trouble. When I turned off mine, the connection speed was restored for the others! (no one of us was downloading/uploading/cloud synchronizing anything). Their laptops had Windows, but one of them had Ubuntu 12.10 on a partition. So he booted into it, and still his connection was slow. When I disconnected from the LAN, it was ok.
Today another friend came at my house (running windows) and we are having the same trouble. When I d/c from the LAN it's ok, when I am online his internet is slow. So that means that it wasn't a problem with my friend's router (last night).
I am concluding the my pc is causing the trouble. I even downloaded avg for linux to search for viruses - it didn't find anything.
Any ideas what might be the cause? A newly introduced bug?
Note: I checked the monitor program and I wasn't downloading/uploading anything (~1Kbps download, ~0 upload)