I thought that Races of Stone was probably the most disappointing book that I've purchased in years. Very 'blah' to me. As a result, I haven't picked up the other two, though I have flipped through them both.
Races of Destiny didn't tempt me at all when I looked at it, though to be fair, I barely use mixed races, wasn't interested in illumnians based on what I saw in the preview, and didn't see the need for a generic treatment of humans, so it would have been a pretty hard sell.
I've only recently, and briefly, seen Races of the Wild. Again I had little interest in it, since I've had plenty of elf books over the years and didn't currently have any elves or halfling in my party, but when I looked at it, it seemed more intersting than the others. Now we've just had a new player who rolled up an elf, so I'm slightly more likely to buy it but I'm still feeling burned from RoS and am hesitant.
I'm not currently running Eberron, but I have been following the line, and I think Races of Eberron sounds promising, though I would rather have seen WotC billing it as an Eberron line book rather than part of the Races of... line.