What do you make of this:
ENCWCSVR.EXE is a primary piece of Encarta Web Companion. You should verify this and see it is installed under Program Files/Common/Microsoft Shared/Encarta Web Companion.
The EXE does not always run in memory and definitely does not kick off based on you performing alot of web searches.

It appears to start up when you are not using your machine for a long time, 30 minutes or more and then seems to be indexing your hard drive. The EXE is pretty agile and when you CTRL-ALT-DEL it stops before you can catch on to what it was doing. The thread can be killed and you'll notice your system runs alot better.

After reviewing Microsoft's vague documentation, some kind of reference is made to web companion searching your hard drive. Well the only way for that to work effectively is if it indexes your hard drive. System performance drops about the same as if the indexer service is running so this is believable. However I do not see much in the way of Web Companion offering a real search across your HD to the end-user. So I suspect they didn't finish the functionality, it was full of bugs or they plan on claiming it is a new feature next year.

My recommendation is, if you aren't actually using web companion then get it off your PC. With the latest push by Microsoft to micromanage your PC you have no idea if they'll pulling a Sony on you.
I just got that off of Google, so I can't swear by it's accuracy. However, it would probably be worthwhile to kill that process and see how the PC performs then. If it actually does index your drive like the poster claims, that would definitely kill performance.