I have absolutely no regrets in purchasing the MW600. Firstly, it pairs flawlessly with the iPhone 4 and I experienced NO drops at all throughout my usage. I can even leave my phone in the living room while listening to music through the headset from my kitchen (which is in a different room), and there was no degradation in sound quality at all.
Sound quality is AMAZING for a bluetooth device! It comes with a set of short length Sony Ericsson headphones, which works just fine (nothing bad about it). But I switched them with my original iPhone earphones and was blown away with the increased clarity and deeper bass it could produce, basically everything gets amplified with better earphones plugged in.
The caller display function works like a charm; when I receive a call it first displays the actual phone number on the OLED display, then after a few seconds it displays the name of the caller based on my iPhone's contact.
The clock on the MW600 automatically syncs and displays your phone's current time.
Now for the radio, I was expecting it to be rubbish for such a tiny device, but it performed so well; easy to autoscan for stations, clear reception with rich sounds.
I really like the volume slider function and don't find it annoying at all, it just takes a little getting used to. Swiping your finger across it allows you to increase/decrease volume and also switch between radio/phone mode (depending which screen you're on). Tapping the slider once activates the OLED screen to display current time etc.
Lastly battery life is great, I haven't switched it off for 3 days now (no charge) while occasionaly listening to music, and it's still at full bar!
This is an excellent top quality product from Sony Ericsson, you'll definitely be pleased with your purchase :)