I host with
www.rackspace.com and I've had 100.000% uptime with them for over 3 years now. They garauntee 99.999% uptime, and have 24/7/365 support. They may cost a bit more, but for a real business, it's well worth it. I have never had to deal with downtime, yet, and are always lightning fast. I can get you $500 rebate if you sign up throught me.
I do host some high bandwidth stuff with Oxeo. A few days ago they were offline for at least 50 minutes during prime time for a security patch update. I don't think any security patch was so important that it required almost a downtime of an hour during peak hours. They could have waited until 3am. So, I do not agree with this. I also do not agree with the fact that they told people it was only down for 10-15 minutes, which is not the case. I had people all over the net attempting to connect to it, as well as ICQ logs to prove the downtime. I am not sure how much longer it was down past 50 minutes since I went home to eat after waiting over 30 minutes after speaking with Oxeo which had claimed 'it will be up in a few minutes'. But, besides for that, they have not been down. The downtime was just a bad decision on their part, which notably is not down time due to their network. I've only been with them for a few months.
That's my experience. ICQ me if you'd like to chat.