It would suggest to me that something in your login items is not compatible with Snow Leopard.
If you don't have a second account then create one.
Login using the second account and see if it is quicker on a 'clean' system.
If it is quicker, note what the standard login items are then reboot into your original account and see what extra login items you have.
Let us know how you go.

regards,
Darryl