Been having random "Server not found" errors all weekend. Anything on the www? No changes on my end of things/setup.

Just here or everywhere? I haven't seen that anywhere. Could be your DNS temporarily acting stupid.

I have one from the public DNS Level 3 (4.2.2.1 to 4.2.2.6) and one from Google (8.8.8.8 or 8.8.4.4) in my Network prefs, in case one of the services is down it will go to the next, and because they are better than my ISP. I get that stupid advertising crap sometimes with my ISP as primary and they are slower. I do let the router grab the ISP just in case the other two aren't working, Anal DNS'ing.

It has been pretty much everywhere. Sometimes they load and sometimes they don't. I've even gotten partial loads with the 404 error imbedded on the page. Strange. Maybe it's local?

What are you using for DNS, default ISP and Network settings?

Might try flushing you DNS cache from terminal.

Currently using my router.

Plug some public DNS of some kind into your Network prefs. See if the problems resolve.

Or you can enter them into the router so everyone benefits.

I'm having this issue at work with the new FAST connection. I had a setting in my network prefs that enabled me to get around this problem ..( I had it before, months ago) and now I accidentally erased that setting while on location with my iMac, the dreaded "pages won't load" problem is back, uglier than ever. The IT guy came by and blames it on everything... bad Ethernet port (ruled out), Safari (ruled out with Firefox, hangs less, but still hangs), DNS ( I changed to Googles 4.4.4.4 and 4.4.8.8-ruled out), tried Wifi( ok) and so on. The pages will just hang. The other day I must have got 30+ Page won't load errors. F'n frustrating when you have a connection that's faster than snot.
Ebay is notorious for not loading.. even CNN.
I come home and it's all fine... with the same versions Safari 5.1.5 and OS X 10.6.8.

Flush your DNs cache first. Reboot too. A reboot is supposed to flush the DNs cache but not if something's fubar with the DNS cache.

Yeah, I have some free time this week, finally slowing down a bit...so I will install Cocktail.