The JamMan is the best practice tool that I have invested in. I've had mine for a couple of years and use it just about every time I practice. I bought the 2gb media card right away. My favorite ways to use it:
- play a chord progression in various keys and then practice soloing, for instance I've been recently learning to solo using maj7, min7 and dom7 arpeggios
- download backing tracks to it and then play along, layering solos over them
- play tunes from my iPod through the aux input and play along
Enjoy, it's load of fun!