>Recently I migrated a 2g 2000 database to 2005 using detach/attach and then fixing all the logins.
>
>When I finished up I looked at the compatibility level for the new database and it was set at 8.0
>
>All has been running fine and I am now considering setting compatibility to 9.0 for the advanced 2005 features. My question: If all has been working well is there any danger in doing this? What is actually changed by adjusting compatibility to 9.0?

There're a lot of changes. See sp_dbcmptlevel (Transact-SQL) SQL 2005 BOL for details.