Suspicious of HD and video card
I've been having this problem too.
Interestingly, I am currently awaiting delivery of my replacement hard drive - Western Digital Caviar Green 1TB - because after this issue started (1 week after buying new computer), I ran diagnostic on bootup and got a BIOHD-8 error.
I mention this because this particular hard drive is advertised to optimize spin speed, seek speeds, etc, etc. I know that my particular hard drive has a problem; not suggesting that everyone's does, but on the other hand you might want to run diagnostic. Couldn't hurt. Adding it up (hard drive special features + sleep issue + my HD has an error) made me curious whether the underlying issue is that my hard drive itself is not properly waking up - perhaps spinning but not reading.
Secondly, I've seen a couple people mention their video cards. I got a GeForce GT 220 (1gb) PCIE card (low rated, but I got it at a bargain basement price), and this (and a couple other) problems SEEMED to start when I installed it 2-3 days after getting the computer. However, the 2-day gap between receiving the computer and installing the video card probably wasn't enough time to really prove anything. Win7 "automatically" updated my driver after I installed the video card, but after I had several crashes, I looked manually and - what a shock - it hadn't updated to the most recent version. Manually updating that driver solved all the problems EXCEPT this "won't wake up" problem.
Originally, I actually was convinced the problem was simply the video card not responding after sleeping, but immediately after I decided to remove the video card and see if that fixed the problem, I ran the system diagnostic. Then, of course, I got the hard drive error, which complicates things.
So I'm about to turn off hybrid sleep and see if that does anything.
If NOT, I'll remove my video card and use onboard video.
If that doesn't work, I'll have to see what happens with the new HD.
I'll try and remember to report back afterward. In the meantime, it might be interesting to find out what video cards everyone is using, and what version of your video driver you have.
Oh yes - when I googled my computer model number plus "won't wake from sleep", I got an HP help page that had a bazillion instructions that were irrelevant, but they did mention enabling your keyboard/mouse to wake the computer from sleep. It's worth checking, anyway.
(From there, the wheels in my brain got turning and I just uploaded the Win7 driver for my particular mouse/keyboard set. I'm sure it can't hurt.)