Yes, it's happened to me plenty of times before. You're not the only one who encounters these database errors, everyone else does too. If I am correct, these database errors are indeed vBulletin database errors. The database errors occur most of the time when people refresh the page every second or minute, like Nica said. Probably because the person is feeling too impatient and really wants to get back onto PC, and I do understand that. Because don't we all wish we could get back onto PC when these database errors occur? All we just have to do... is be patient... and Steve will fix the database.
And I can say the most common reason why these database errors occur... it's because some people don't actually know that when PC is lagging (in other words... acting slow) or crashes that they shouldn't keep refreshing the page... like that message that used to display said:
"If PC is acting slow, go do something else for a while, and then PC should be fine again."
Something like that anyways, I can't remember the exact words though. I do know that I would never keep refreshing the page... because... we don't want the traffic limitation even lower... it's low enough as it is, because if it was lower... it would prevent alot of people from even browsing PC. Which would be really sad if that really did happen.