[mikester]

At a company I used to work for it was quite common for folks to leave and come back. There were a variety of reasons to do so.

Ultimately I would not return to a place to work unless the problems that lead to your departure no longer existed.

I almost went back to one place that I left because they passed me over for promotion after telling me that it was mine. When they offered me the new job it was at the old title and I said 'it seems that you are doing the same thing to me as you did before, you have not learned your lesson - I have learned mine. No thank you.' (in my head...)

I wouldn't worry about the grass being greener unless that was really why you left. If it sucked there and still sucks there then I wouldn't go back.