I have run into this very issue twice now, having previously never seen it before. Unfortunately it's always on customer systems so I can't just wipe the drive and try to reload the OS, because they almost always pass diagnostic testing.
I just took a quick video of the issue this afternoon and sent it off to Apple to see what they have to say about it. I'll post more when I hear back. Not holding my breath for it being anything terribly enlightening, but every now and then they surprise you.
Preliminary indications seem to be that it's just a corrupted OS, because I can swap in a drive from another system and it'll boot up just fine. So it's not an EFI issue or anything with the hardware.
And while it's possible Apple just recently updated its retail discs to 10.6.6, last I checked they were still 10.6.3, and that likely wouldn't work with a Mid-2010 MBP. You'd really need to get a set of the official restore discs, because the Mid-2010 MBPs came out after 10.6.3 IIRC, and so they have a couple of special drivers not in the retail disc. If you call Apple's support line and give them the system serial number, for about $20US or so they can get you a new set of restore media. In any case, when you have issues starting the install media, it's always best to first try it with the restore media that came with the system. Then you can rule out there being any issues with the OS revision.