Your question made me look at the handful of markets currently using PPM (e.g., NY, LA, Chi, SF, Hou, Phil, Long Is). R&R shows the 6+ numbers on their website. So far, it does not appear that Hot AC is showing any meaningful improvement. Moreover, it seems that its more "pure bread" format neighbors, CHR and AC, are doing better than Hot AC with PPM. Not sure why that is though.
You must have not seen the LA numbers or looked at them closely. Hot AC KBIG gained about 74% (3.3 vs a 1.9) when you compare the first PPM numbers (from July) with the Arbitrons from the same period. CHR KIIS saw about a 20% jump (4.9 to 5.9) while AC KOST was at a 3.7 in BOTH surveys!
I haven't had a chance to look too closely at the other markets yet, but from what I've heard, the other Hot AC's (not surprisingly) have seen similar bumps. It makes sense based on the differing methodogies used...
Randy (Kabrich) or David can probably give you a much better and thorough answer to this than me though.