You will see some nice improvements in performance but ... you need to know some things first:
1. Backtrack is a pentest distribution that means it's not like a normal OS with movies or whatever.
2. Install it only if you will use it most time in pentesting if not stick to a Live CD or VMware.
3. Most programs need to be run as root, even if you make an unprivileged user you woun't use it that much so you must know what you are doing because you might sc**w it up.
I use it as my main OS and I'm happy with it but I made a "TEST LAN" at my home where I can play with it ... so if you woun't use it stick to another OS and just use this in VMware.