Comment 42 for bug 523143

I had the exact same problem (Dell E6400, Lucid 64bit) but I had to reinstall ubuntu from scratch to solve it...
Wifi was enabled if I booted with the hardware switch in the off state, but it didn't work if I booted with the switch in the on stated, and when my laptop resumed from stand-by, the wifi could not be enabled.
However, the bug reappeared yesterday and I just did the rmmod dell_laptop, and wifi came alive again!!

Thanks!