First of all, if you don't know, Aircrack is a program that's used to crack encryption keys of wireless networks. My laptop has a Broadcom 4306 chipset, which has been hacked to death by Linux developers.
Starting with kernel 2.6.24, a different driver is used for Broadcom chipsets (the older one was based on Intel drivers, the new one I believe is based on MadWifi). The drivers in the new kernel support injection out of the box, but the older ones do not. I previously spent a lot of time patching the older drivers to support injection, and it worked well, until I upgraded to the new kernel.
At first, injection only worked if I moved my laptop very close to the wireless AP. That problem appears to have been corrected in the new 2.6.27 kernel.
For a long time, I thought injection didn't work at all in the new kernel because I was doing it wrong: I was trying to authenticate with my access point at home, which uses no encryption. Apparently, the AP you authenticate with using Aircrack has to use WEP. Then today I tried authenticating on my neighbor's WEP-protected AP (just to test it, of course :) and it worked!
However, before doing that, I worked hard on making a live Ubuntu Gutsy CD that includes Aircrack, Kismet, and the patched drivers. So for anyone that wants it, you can download it here!