The SharePoint Timer service is handy for what it does but it occasionally gets very hungry and devours hundreds of megs of RAM and keeps it for hours. This isn't a problem on most production environments because of the memory those machines typically have but it can be a killer on a memory challenged dev Virtual Machine.
The most common symptoms that I've run across is that starting Visual Studio in Debug Mode takes 2-3 times as long as normal and stepping through the code is painfully slow. When this happens, I restart the timer and all is well again.
I used to do this from the Control Panel but found that there is a much more efficient method: use a batch file with the commands below and just run it periodically. I have a shortcut to this in my Quick Launch menu and run it before starting any development.
net stop "Windows SharePoint Services Timer"
net start "Windows SharePoint Services Timer"
Of course, if you happen to be doing work that doesn't rely on the Timer functionality (which is most likely the case) then you could always turn off the service and avoid the problem entirely.