[fallen1]

There has been a lot of talk in the Steam forums about people suddenly getting much lower fps since the update. I've also seen a lot of complaints about people suddenly getting a lot of choke and loss since the update, both of which can really kill your fps.
I've also seen (both personally and in various forums) apparently random instances where after a Steam update something had changed in the graphics settings for no apparent reason, so you might want to double check to make sure none of your settings have suddenly changed.

Aside from Steam screwing up with another update, there are a couple of possibilities. First, check to see if there is an updated version of your graphics driver. There have been a couple of times where I've gotten a pretty impressive performance boost just by updating my video driver (the difference can be really noticable if your current driver is several revisions old).

Also, like Ghost said, defrag and dust out your computer. If your computer is constantly sifting through file fragments or building up too much heat your performance will plummet.

You also might want to run a couple of anti-spyware apps to make sure you don't have a spyware infection sucking up CPU cycles and bandwidth. I always reccomend using at least 2 and preferably 3 different anti-spyware programs since there is no one program out there that catches everything. I have Ad-Aware Personal Edition and Spybot Search and Destroy (both free) that I use to supplement Webroot SpySweeper (not free, but worth the money).