Jim Forbes runs a website devoted solely to the Selectric Typewriter. Politically, he describes himself as one of those "anyone-but-Bush people." But in terms of RatherGate, he says: "For those who want my opinion...the documents appear to be done in Word, and then copied repeatedly to make them 'fuzzy'."
And this site makes a plausible case that the Killian signature is not forged or fake, but rather sloppily cut-and-pasted.