SQL server 2005 comparability mode

Hi there, 

Dont know if this is the right forum for this... anyways

We are planning to move our DB running on SQL 2000 to 2005. I am aware that by default, db attached to 2005 from 2000 are in 80 compatibility mode... 

I wanted to know If someone has used the DB in this mode? are there any major problems associated, or risks of running a DB in 2000 compatibility except the exemption of some of the 2005 features?

Also is it still possible to purchase Windows server 2003 R2 Datacenter edition

Thanks

Saad