I switched over to
Servint.net this past summer after a major meltdown at my previous host - so far I have been very pleased with the 24/7 support system. I have had to contact support a few times, and problems have always been handled promptly and competently. If you are on a VPS, upgrading your server can be done with practically no downtime at all. From what I can see on the internal support forums, there are quite a few customers running vBulletin boards.