Awful Network Performance
Several things:

Do a TCP Dump to analyze traffic, to see if you're machine is hitting sites that are bogging it down. At the command line, type sudo tcpdump -i en1

Do a DNS cache reset. At the command line, type sudo dscacheutil -flushcache

Check the MTU settings. Confirm with your ISP what the MTU setting should be, and then go to System Preferences -&gt; Network. Find your connection and click Advanced. Find the Hardware tab, and enter the MTU setting manually if it does not match.