I've noticed this myself. Any idea why that happens?
I've noticed that sometimes adding a blurred shadow disables sub-pixel anti-aliasing, and sometimes that makes things look better. I think, though, that there's a separate effect that makes the font look thinner when a blurred shadow is added that I don't really understand.
What browser is that in, and do you have anti-aliasing enabled in your OS? The 'original' text in your screenshot isn't anti-aliased at all, which I don't think should happen unless you have AA off on a system level.
You know what, it just dawned on me that at one point I had my IE7 ClearType disabled because I didn't like it's smoothing effect. I don't know if that setting is carried on to Chrome or not.
AFAIK, ClearType settings apply system-wide. It should be pretty easy to tell though; if any non-image text in your browser is smoothed, it's on. If it's not, it's off.
What it sounds like the white drop shadow did in your case was simply force ClearType on for that text.
Additionally, if you're looking for higher quality fonts, the same guy (Ethan) who runs the squirrel runs a boutique for @font-face fonts: http://fontspring.com
Suggested feature for a @font-face site: include a sample of the font using @font-face for browsers that support it, instead of just images (at least I didn't see any live samples).
If you use any exotic type for your @font-face, be sure to give it a text-shadow: 0px 0px 1px #fff; to smooth out the edges.
The shadow colour should be the same as the background colour. So technically, it's just a smoother, not a shadow.
The result is the same smooth render you would get with sIFR. Works wonders.