Hi, lets say someone links to your site like: http://somesite.com and your url is redirected to http://www.somesite.com. Well page rank will be passed on to you?
If I remember correctly, a 302 re-direct will pass over serp results too (but I'll have to check up on that) Thus it can give you a bit of time to work on your rankings, then do a permanent 301 re-direct. Brad