Server Load is Bad

I got this note from my web host:

Your site is taking up an excessive load on the server's processor @ 142% (more than one processor) and is slowing down essential server system processes and other client accounts. This is a serious issue. The load is too high for a shared server account. Please reduce the load of your site within 48 hours by code optimization, replacement, caching, updating all scripts and patching security holes, prevent spammers/bots, reducing db sizes and/or disabling features/modules to avoid account suspension.

I don't know what's going on. My traffic has nearly tripled since the first of April, but even that shouldn't affect server load. I have to figure this one out. If iFlipFlop goes down for a few days then you'll know that I didn't quite figure it out in time.

Spambots, anyone?