From time to time, we see someone has inqury about the H-1b transfer. A lot of time, a lot wrong information circle around the net, especially when comes about if the "receipt" is a necessary. The truth is that after you file your H-1b transfer petition, you may work, even without the receipt.
Just one advice: before talking about legal or illegal, know the law first. If you don't know, don't mislead others.
Here is the info you can check
http://www.h1base.com/page.asp?id=41
H1b visa TRANSFER
** H1B visa holders can change employers as soon as a H1B petition is 'submitted' to the INS by the new employer **
New H1B bill approved in the senate and House
The senate voted 96-1 to approve the new H1B bill S.2045
The House of Representatives passed the H1B visa bill (S. 2045) on a voice vote.
H-1B nonimmigrants may change jobs upon the filing of a new petition by the new employer as long as the individual is in lawful status at the time of filing and has not engaged in any unauthorized employment since his or her last lawful admission
Allows individuals who have filed for adjustment of status and whose cases have been pending for 180 days or more to change jobs or employers without affecting the validity of the I-140 or underlying labor certification, as long as the new job is in the same or a similar occupational classification to the job in the original petition and labor cert.