This is mostly for my own reference, but may also be useful to you.
My MacBook has been afflicted by an issue whereby the root process syslogd uses up excessive CPU time. Thankfully, there’s a reasonably straightforward fix on The Mark Bao Weblog for those who are reasonably au fait with the OS X Terminal, and it certainly solved the problem for me. That said, your mileage may vary – this is one solution to a problem potentially caused by many different things; a Google search also brought up potential issues with iDisk, Back to my Mac and Time Machine.
I’ve had a few issues with the MacBook getting too hot lately (while playing World of Warcraft) so hopefully the fact that both CPU cores are not working flat out will mean it runs cooler. And make the battery last longer.