just got it installed yesterday. this little sucker rocks. the following comparison tests are based on airodump-ng power ratings. all samples approx. 100' from AP:

Presario w/built-in 15
Atheros chipset
(no ext. antenna)

Compaq Evo N600c 34
w/Linksys WGUSB
& rubber ducky

Evo N600c 120
w/Alfa & rubber ducky

Evo N600C 125
w/Alfa & Hawking
directional ext. ant

Evo N600c 132
w/Alfa & cantenna

Still working on installing Backtrack on the Evo. Some problems partitioning but I think this is due to 4,000 cylinders on the drive and should solve it soon. Interestingly, whilthe drivers from Taiwan compiled and worked fine, aircrack-ng would NOT show power. But with the Backtrack 2 c/d, everything worked perfectly.