That is the problem with this issue. Some people have a genuine hardware problem. But 90% of the no wi-fi posts are because the machine is booting into Safe Mode.
Did you do a fresh install or an upgrade? Also, did you hook up the LAN cable and download the latest firmware, 10.7.1 update and the wi-fi fix they just issued last week? If you have done a fresh install, have all the latest updates and firmware, your bluetooth devices are off during boot, then you have a genuine hardware problem or the Mac is still booting into safe mode.
Look at the above post from Alexander Leong, and check the picture of the bootup screen.
If you see that progress bar during bootup then your Mac is booting into safemode (and it will say no wi-fi hardware installed). If you do not see that progress bar and your Mac boots up quickly and normally, yet your wi-fi is still not working, then you have a hardware issue. Try resetting your SMC and PRAM, and give Apple Care a call. If you upgraded I would also suggest backing up everything, and doing a fresh install by reformatting the HD. You can boot into the recovery parition and do this, but I will tell you I still have this issue when the BT devices are on when booting. But the fresh install cleared up a lot of GUI glitches I was having.
I run an English language training school in China and use Macs with Rosetta Stone every day. This issue only occurs on my 2010-2011 models after installing Lion and booting with the bluetooth devices on. I have never had any issues with my Mac Minis or Macbooks, only the iMacs and one Mac Pro.
However, I will suggest everyone to reset the SMC and PRAM after upgrading to Lion. Most of my iMacs had a noisy fan or the fan didn't run at all after installing Lion, and resetting the SMC and PRAM took care of the issues.