I agree with charity-crafter about trying one before you buy it. I have three friends who have a Go! or Baby Go! Last summer I bought the drunkards path die and borrowed a Go!. It let me use the machine without spending the money and taught me that I probably wouldn't use the machine enough to justify the expense. One of the girls is using it primarily for the applique shapes. The other uses it to cut scraps into geometric shapes. The third gal hasn't used hers much, but then she's hasn't had much time to spend sewing in the last year.
After using the machine, I doubt I'll buy one, but if I ever decide to make something with curves (DWR) or strong angles (blazing star), I'll buy the die and then borrow the machine.