I don't know what's going on, but I've observed some font weirdness with OS X today. I sat down to read my usual sites and stuff, and I noticed all on-screen text looks lighter and crisper than it did before! Safari, the Finder, everything. Was it like this yesterday too, or did I just not notice until today?
I've always had my iMac G4 font settings set to "lighter", because I thought the other settings were too dark. Now, I'm setting it back to "medium" because everything is lighter than what I'm used to.
Not that I'm necessarily complaining. For example, I always thought the bold text on the menu bar where my username is written was oddly heavy and not quite anti-aliased correctly. Now it's perfect.
I can't imagine what caused the change. I did finally update from 10.4.6 to 10.4.8 a week or two ago. Yesterday, I installed several new fonts. In neither case were any immediate changes apparent. I also recently re-calibrated my screen, and that could be the most likely culprit even though I didn't notice any instant difference.
Has this happened to anyone else?
Edit: I found an older screenshot of my menu bar and compared it in photoshop to my current one. There are indeed differences. In particular, the intensity of my Mac's sub-pixel antialiasing (which is evident as coloured pixels when you zoom in) has been reduced a little.