I recently had a problem with my Dell laptop (XPS M1330), where the wireless was no longer working after upgrading to 9.10.
My network applet was showing that the wireless was disabled, as was 'lshw -C network'.
Thank you to Chilli555, who found the problem. There is a bug which is causing rfkill to see the wireless as turned off via the kill switch when in fact it is not. The bug has been reported here: http://bugzilla.kernel.org/show_bug.cgi?id=14098
To see if you suffer the same problem as I did, try this. If your wireless springs to life then you do!
To fix add 'blacklist dell_lapto' to /etc/modprobe.d/blacklist.confCode:sudo rmmod -f dell_laptop
Original thread here: http://ubuntuforums.org/showthread.php?t=1375942