I just came across one of the most useful posts on developer.force.com that I have ever seen:
Jesse Lorenz provides full instructions (along with a best-practice) on deploying quickly from one org to another using the Eclipse IDE.
Read it at http://wiki.apexdevnet.com/index.php/Deploy_Force.com_Applications_Faster. You’ll be glad you did.
[Update: Jesper Joergensen just wrote a super follow-up on deployments in the upcoming Winter 09 release at http://blog.sforce.com/sforce/2008/09/set-up-orgs-4-t.html