I'm afraid you can't do it easily, you'd have to mod the Launcher2.apk to enable bold text, however you could always try pushing a Launcher2.apk from an older release when the text was as you preferred it... I don't know if it'll be as stable but it should work. Give it a try and let us know how you get on
Dear Sweebee & GUSTAF,
I had the same problem too. Now I'm using version 1.5.13 and I dont like how the font looks now. I figured how to change back the font to Arial Bold (I googled, asking at another forum, but no one can answer this) until I found this thread.
I try to extract the launcher2.apk from MIUI 1.5.6 zip file and placed it in my SD card root, and try to install it from File Manager, but at the end, the app says "Application NOT Installed".
Then, I make a zip file for launcher2.apk and placed it again in my SD card root and try to install it from recovery mode (Install from zip menu), but still nothing changed.
So, by the way how do you install it? Im using HTC Desire, but so far I haven't touched the S-OFF.