sigh, so many PROFESSIONALs discussing such a MEANINGLESS topic!
It is so clear that you have to rebuild the tablespace after your offline the datafile.
Offline drop the datafile only allows you to open the database temporary so that you can export/move the tables in the tablespace and drop and recreate it later.
I think the metalink note has said it clearly.

nagarjuna:
Your way of removing that datafile is TOTALLY WRONG!