I've never been a fan of using mixed bold and normal fonts in development editors. Mostly because I had fairly ugly experiences with editor configurations that used bold fonts for things like keywords: it usually ended up that things didn't align properly, or, worse, the caret position didn't reflect where the caret was actually positioned, which made things very annoying.
However, I did found out yesterday that this was not a problem with the editors themselves, but rather with my choice of font. As it turns out, Lucida Console, which is the only really decent monospace font included with windows, does not really work well in this kind of environment. Courier New, on the other hand, works fine with bold and normal formatting, but who in their right mind would choose to use Courier New? :-)
Fortunately, I found two other fonts that work just fine as well: Bitstream Vera Sans Mono (you can see an example here, if you're not familiar with it), and our new favourite Consolas (included with vista and Office 12).