I have the 3510 since the day it came out. It has been frustrating at times essentially being a beta tester for them. I have no clue how they released it, I'm sure they knew what the problems were. My complaints are in that digital home thread
If the Gateway isn't for you (which has it's own issues) I would still buy the 3510 as for me I knew I'd be kicking myself in 6 months if I bought the 3400. So either experience the 'bleeding edge' or wait 6 months to buy it.