I have the Onguard Bulldog Mini 7 (looks similar to Collen C's). I attach mine underneath the top tube using the twofish bikeblock. The mount the lock came with wasn't well made.

I used to to have the Onguard Brute, but it was to heavy and clumsy that I hated bringing it with me. The mini is pretty light and like any lock, works as a deterrent. I also have some Bikeregistry locking skewers for the wheels and an old chain locking my saddle to the frame.

Never underestimate what a thief will take. I've had old saddle bags taken when left unattended for about an hour. I also had my nice saddle taken .

What kind of Jamis do you have? My first bike that I bought with my own money is a 1999 Jamis Exile.