Unfortunately, I may be the guinea pig. My 07 Chevy Avalanche was broken into this week and among many other things taken was my beloved Zumo 550 hidden deep in the console. Any Chevy owners with an Avalanche type door handle be warned ---- very easy to manipulate. An 07 Yukon close by was also broken into that day. Anyway, I'll be replacing the Zumo as I really liked it but will take a hard look at the 660 v 550. Right now by just reading the comparison, I can't see moving to the 660. With XM already on the SEUC I don't need the option, but am hoping to use the bluetooth in the future when I get the Nolan or J&M setup. I don't understand why the 660 is limited to 10 routes, and also liked using a full size SDHC card on the 550 for tunes and data rather than the mini card. Unless I learn some hard reasons to convert to the 660, I may try and wait for the expected price reductions to the 550 as seen with the phase out of the 450. What would you do???