I took the following from H1 transfer FAQ section:
Q: Can an H1b that was approved and never used be transferred from outside the country?
A: A transfer is nothing but a new H1b application that is not subject to the cap. If you have proof of prior approval (like the copy of I797 or a receipt number), a new employer can transfer the H1b even if you have not entered into the USA.
My question is, I have an approved H1B petition (I-129/I-797 valid till Jun 2011) for company X. I quit company X last year and joined company Y. Is it possible for an US company Z to recruit me, get this H1B transferred and get me to work in US?