Sound: the sound is very good (yes, I know this is subjective). Bass is present and actually has some presence, treble doesn't roll off noticeably at the top end even over bluetooth which surprised me. Overall the sound is very clear, neutral and natural -- it doesn't get wearing over time.
Fit: I've had any number of headphones over the years -- mostly Sennheiser but not all. I've a pair of closed HD250s and I've had open headphones and stick-the-rubber-in-your-ear headphones and the 210 BTs are the most comfortable I've known.
Wearability: walking around, you don't get that under-water effect of the rubber-plug style in-ear headphones, and wind-noise isn't exaggerated in the way those headphones do either. The 210 BTs block out enough sound, but not so much that you feel completely cut off (you can tell when someone wants to talk to you for example -- a good thing).
Wireless: I'm surprised at how much more wearable these are because of the lack of wires. Nothing catches, nothing drags, nothing pulls the phones off your ears, and yet the headphones are the right weight (i.e. light).
The wired connection, on my Google Nexus One, sounds about the same as through the bluetooth connection. I suspect that (as with other low-power devices) the headphone amp in the phone isn't really high quality so there's probably some roll-off on the high frequencies -- but it doesn't sound muffled. When you're using the bluetooth connection you're bypassing that headphone amp in the phone, and the sound is about the same -- impressive.
I'm really surprised -- I wear these phones at work and at home now in preference to supposedly better wired ones. They're comfortable, the sound is neutral and natural and doesn't become wearing over time, and when someone walks into the office to talk to me I tap the pause button on my right ear and slip them onto my neck -- walking off with them still in place if I like -- no wires.
Lip sync: for me, there's about 1/8 of a second of lag when watching video on our iPad. On my MacBook Pro there's no lag. And of course for music a slight lag isn't a problem.
Seriously, these are good. By the way: if you want to be able to hold phone conversations with them then these won't do that -- you need a pair of Sennheiser MM 400 'phones for that.