If the internet seems dead, it may just be your DNS
From time to time, my ADSL internet connection goes down. Things time out (or they're just really, really slow). I've found that more often than not this is due to DNS failure. Host name resolution times out. If you happen to have a few IP addresses lying about, then they actually work.
For this reason, it pays to have some backup DNS. There are several free DNS services. Right now, I've added the following two DNS servers to my DNS configuration (Network Preferences => Airport => Advanced => DNS on OS X). They are both from OpenDNS:
It's also quite useful to keep a static, stable IP address around for testing when DNS isn't working. If I ping google.com, I get 18.104.22.168. That'll probably do. :-)