If you are reading this, chances are you are running a RT2500 based chipset wireless card that worked perfectly with Ubuntu Edgy and then stopped working after your upgrade to Feisty.
Read the help here
How do I know if I am using a RT2500 chipset?
In Ubuntu Feisty, go to Applications, accessories, then choose Terminal. In the command line, copy and paste in the following.
If you are using a card based on the RT2500 chipset, you will see something like:
ra1 RT2500 Wireless ESSID:blah Nickname:blah,blah
Now you know that you are using a RaLink card based on the RT2500 chipset. Okay, lets keep going.