I had the same issues with KIS 2010. It slowed everything down - especially internet browsing. I tried several other products, and I ended up really liked Symantec NIS 2010.....however it crashed several times and I had to reinstall it. After the fourth time it crashed I decided to try G-Data since it rated tops on detection and its 3-user license was only $39.95.
So far I really like it, but it does have some issues:
1. It takes much longer for full scans compared to other products.
2. If you install the trial version and decide to purchase it you have to uninstall it and reinstall it as it will not recognize your password/key (very stupid if you ask me).
3. Since it a dual engine scanner it takes more resources - I only use engine A (Avast's engine) on my laptop. I use both engines on my desktop without any slowdowns.
4. They are based in Germany, so there is no U.S. based support. However they answered my email within a few hours.
UPDATE
I now have both engines enabled on the laptop with no issues. For some reason the HP Windows 7 driver for my web-cam that loaded on start-up was constantly eating 40 - 50% of my CPU cycles. I disabled it and there is no noticeable slowdown on the laptop with G Data running full-force.