I was recently experiencing very slow wifi connections in Kubuntu 10.10 on my HP Pavilion dm4 with an intel wireless card. I was getting intermittent speeds from 0.3 to 1 Mps. Needless to say this was driving me nuts. After hitting the forums and verifying that this is a documented problem and reading the various solutions I installed
linux-backports-modules-compat-wireless-2.6.38-2.6.35-28-generic
and linux-firmware version 1.38.6
Note: if linux-backports-modules-compat-wireless-2.6.38-generic is available install that instead.

Well, after installing the above and rebooting I am getting between 8 and 10Mps down which is faster than I get in windows.
Problem solved and then some!!!