Since I upgraded from Ubuntu 10.10 to 11.04, my internet connection is as slow as hell. I have tested my other 10.10 machine and it is just as quick as the first one was.
What has happened? Why is the maximum download speed now 30kb/s instead of the 2.5mb/s I used to have?
I've found out the problem; it's some sort of problem with my wifi driver (ath9k) which was resolved with a simple command:
sudo -s
echo "options ath9k nohwcrypt=1" > /etc/modprobe.d/ath9k.conf
Enabling the dma64 option helped for rtl8192e
echo "options rtl8192ee dma64=1" >/etc/modprobe.d/rtl8192ee.conf
I had the same issue, but only after upgrade to 11.10. Either way, neither echo "options ath9k nohwcrypt=1" > /etc/modprobe.d/ath9k.conf (s/9/5 if you're using ath5k) or disabling IPv6 (another solution floating around) helped.
What did help was changing the encryption on the network from WEP to WPA2 (inspired by a forum post I can't find at the moment on a related issue where encryption slowed down a wireless connection). It's still not as speedy as some of my other computers, but a whole lot better than it was.
