Valve has confirmed that they are indeed working on an anti-cheat proggie. Here's what was said on the HLDS mailing list:
Unfortunately, I can't give out more information. We're aware of the current problem with cheating and are working to find a solution. We play on-line and are just as frustrated by cheaters as you are. We're working to implement a long-term solution, and coding for that has already begun. This will involve many phases of attack. I'm sure you understand why I can't give out the specific details of our strategy.What that means is that it won't be one huge roll-out of the perfect cheat-prevention, but will come in small doses. I'm looking forward to it!
However, it WILL NOT be "a year or so" before we start releasing cheat-prevention code. We'll be phasing it in during future updates.
-Eric