Well, this thread has gotten quite a bit of attention...
Nothing has changed except I keep loading more and more things into my projects. I use FL as the host and usually have some random VST instruments thrown in, like EWQLSO Silver, Plugsound, Sytrus, and a couple others. I use DirectWave for a sampler since it works pretty well and it came with the XXL version of FL anyway.
On one of my newer songs, I've got about 35 channels, about half of which are VSTs with 1-5 effects in the mixer or on the plugin itself. My CPU usage is about 30% and there is a lot of crackling during some parts. How much more performance can I expect from something like a Core 2 Duo? Let's say one that runs at around 2.8 GHz.