Outside of salary issues....

I have noticed as a contractor you are sometimes treated as a bit of an 'outsider' in a team. This can be kept to a minimum if you make an effort to get involved (sometimes beyond the requirements of the contract) and don't act like a 'contractor' (eg. clock watching, penny counting, clocking in and out bang on your 8 hours). But to a certain degree it inevitable to feel bit left out when your development is not invested in and to the company you are just a number on a spreadsheet.

It also obviously depends on the company. If you're in a group with lots of other contractors, then you won't feel so different. If everyone else is perm and you are the only contractor, you might be looked 'down' on a bit.