I've had my 55EX500 for close to a week now. So far, I'm very happy with the set. The blacks are great and the lighting is as far as I can tell, very uniform - no flashlighting that I can see. I'm also pretty happy with the color.
As far as issues go, I've noticed some delay/lip synch issues that I didn't have with my previous set (KDS XBR1). I've been able to compensate for this by adjusting the delay setting on my receiver so not that big of a deal. I'm not sure if this is the same as input lag. As I mentioned in another thread, I also see rainbow like patterns when light directly reflects off the screen that can be a little distracting (see attached pic). I haven't noticed this on either of the other 2 LCDs I have (Vizio & Toshiba) so it must be due to Sony's anti-glare screen (polarized??). I'm curious if the V series had this same type of screen or if this is a new panel being used in the EX line. The picture seems to be a little grainier than I was used to on the XBR1 and the sound quality, while not bad, isn't nearly as good as the old XBR1.
Overall, it seems to be an excellent TV and a good value especially for the 55EX501 at the price I've seen at Costco with 3 year warranty. I know the 500 is a ways from the top of Sony's lineup but based on other sets I've seen, I really don't feel like I'm missing out on too much.