I'm glad I found this... I thought I'd burnt out my 644 and even placed an order for a second one this morning. After reading this, I replaced the resistors and was able to reflash my Fuzebox. Ladyada, you should really add a note about this to the "programming for the first time" page on http://www.ladyada.net/make/fuzebox/upload.html.
hm, i thought i did. but it looks like i didnt. which is odd. anyways, the usbtiny was ORIGINALLY -only- designed to program spokepovs. the 'it can program chips' thing was kind of an extra! but then, it turned out people really wanted that instead. (oops)