I'm considering a U310BT because its price is only about $50 more than a regular CD receiver with built-in bluetooth capabilities. I've read a lot of bad reviews on the U310BT, and I'd like to check here to see whether or not it is a unit to avoid.
Problems that I've read about...
Navigation - Some reviewers post that the U310BT takes you on inefficient, roundabout routes to your destination. Is this true, or has this problem been solved with software updates?
Bluetooth - Inability for other caller to hear well while making and receiving calls using the U310BT? Do you all experience the same?
Long boot up times and frequent freezing
I have been using it for almost 10 months. For the current price it is going, it is really enticing( ofcourse there is a reason why it is being sold so low).
It depends on what priorities you have.
Boot time is not a problem for this unit, because unit always goes into Standby ( Suspend to RAM) mode.
No GPS:
POIs, No Gas Stations, No Restaurants.
The routing itself is not bad, but the Navigation database is worst. It does not even have the addresses of 6+ years old communities, not even major Bus routes. If you are lucky enough to find the address you are looking, then it may be reasonably good.
You can not bypass any roads on the route. Depending on road you are ( esp any State Highways) it does not even show the exit numbers, no cross street info. Latency, and wrong location are not uncommon, so it is not wise to depend on this for any downtown travel.
Music: It is good, except you can not play from SD card. The screen usage is very in-efficient, can only show 3 lines from usb/iPhone/iPod/CD.
Using the Joystick control is tricky, esp while driving it may drive you nuts... 
Bluetooth, be ready to replace the supplied mic, but overall quality is ok(not bad), but not as good as many OEM solutions.
Do not expect unit to use as portable GPS, as it is not( GPS is in main head unit, not in detachable unit).
Even with all this problems, I think it is still $250 worth ( vs $400 I spent).