I don't know why you are running ClamXav.
There is nothing for it to find and it could cause
problems as well as use CPU cycles.
I'd dump it.
When the first MacOS X virus is out there you'll hear
about it in the Mac community.
ClamXav doesn't use 'CPU cycles' - running without the sentry enabled causes it to do nothing at all unless and until set to scan specified directories by schedule or manually, and with sentry running, it triggers scanning only when the contents of the specified directly changes, and then only the file(s) that change. When it does that, the CPU load typically rises to around 3-4% (often less than 2%), and then only for the duration of the scan of the changed file(s).
As to there being 'nothing to find', that isn't so. It's capable of finding infected emails, and thus help ensure that the Mac user is not assisting in the propagation of malware to PC users, it can identify malware in scripts, identifies many of the phishing scams that lead to identity theft and which are platform independent since they rely on fooling users into reacting, identifies and removes macro viruses that can impact Mac users, and identifies a number of Trojans which it is otherwise easy to pass on to PCs.
Running ClamXav is a matter of taking reasonable precautions, being responsible within the community of users as a whole -many of whom ARE vulnerable, and of being prepared for the day that malware for MacOS starts to appear. It also has to be said that if all Mac users take the view that their systems are safe and thus no malware detection software is needed, the only way that we will ever know of a threat is if the commercial organizations who sell defensive software tell us they have found something. They have a vested interest in there being a problem to find, so are not all that trustworthy. Not only that, but by the time users buy, install and use defensive software after it is announced that malware has been detected, it's entirely possible for a virus to have spread like wildfire among Mac users and to have done considerable damage.
It may be that many Mac users either don't want to run, or see the need in running, defensive software but there are those of us who do, and suggesting it's a bad idea to be prepared is perhaps a little misguided.