Is it best practice to detach user dbs during sql2005 IN-PLACE upgrade from sql2000?  If it is, after upgrade (setup.exe) is successfully done, will re-attach the user dbs to the newly in-place upgraded server then act like the side-by-side upgrade where we restore/attach user dbs? except that we don't worry about instance name, jobs, login..etc.

In anycase you have to keep a backup as a rollback strategy whether it is backup file or detached file does not matter. So detaching DB and then attaching should also work.

Madhu