When I executed the Sleep Checker app, it told me that CUPS was preventing sleep. So, I deleted all the unused printers that I had there, and now OS X Lion Sleeps fine.
I hope this tip can help other as it did helped me
If your PC sleeps, but reboots at wake try this:
<key>Kernel Flags</key> <string>darkwake=0</string>
If your CMOS resets after Wake then patch AppleRTC:
sudo perl -pi -e 's|\x75\x30\x44\x89\xf8|\xeb\x30\x44\x89\xf8|; s|\x75\x3d\x8b\x75\x08|\xeb\x3d\x8b\x75\x08|' /System/Library/Extensions/AppleRTC.kext/Contents/MacOS/AppleRTC
If you have other problems with Sleep, then it might be related to dsdt and USB ports not being set up as internal.