yes, it is node locked to the machine (how else would i know your machines from your buddies)
there is a FAQ: http://solidice.com/keyclone/faq.html

i try to explain the normal questions (although, i really need to do something with the website... i've spent my time on giving updates...)

of course, there is no limit to the number of wows on a single machine... the limitation is your hardware.
before keyclone, hardware multiboxing is all you had... and that was very pricey