Hi Spinner - I am having this same issue and just wanted to share my experience for your information.
In short, I began having the same issue after the HS upgrade. I performed a myriad of troubleshooting tips (SMC reset, PMU reset, reinstalling HS, safe mode, hardware tests, disk utility, etc.). I even waited for the first major HS update hoping this would resolve the issue. After a number of chat sessions with Apple, I finally took my MBP into an Apple Store Genius Bar. They performed all kinds of hardware tests and other functions and everything checked out fine. After all of this, they said the next step was to do a complete erase and install of HS. We did this with the help of a Genius and I am still having the same issues. Since there was nothing wrong with the hardware, this definitely seems to be a software issue with HS and there are other web forums which mention the same issue.
At this point, unless you do have a hardware issue with your mac, it is probably best to wait for the next HS updates to see if this works.
The other recommendation that I have would be to submit an apple bug report at https://bugreport.apple.com. You can register with your Apple ID and it is totally free. You will be asked to answer some questions about the issue and upload some logs from your computer. The process only takes a few minutes and this is probably the best way to get this issue resolved for future updates. The ideal scenario is to replicate the issue and then take a system log as soon as your restart your computer. You can attach these files to the bug report and keep sending them in as your issue occurs. Apple is definitely checking these and can hopefully incorporate fixes in future HS updates.
Good luck and I am definitely feeling your pain as this is getting increasingly annoying and frustrating. Mine is happening at least once daily if not more.