Changing Compatability From 65 To 80

Finally, I may have a good enough excuse to justify changing the compatabilty level of one of the biggies I look after!

Before I go ahead with the change I just wanted to run a couple of questions passed the community.

I know this is very vague, but what sort of problems should I expect? I know there are a few syntax changes, but I don't imagine I will have a problem going up in compatability level!
What is the best method to perform this?
A very simple

EXEC sp_dbcmptlevel 'playdb', 80

Or

ALTER DATABASE SET SINGLE_USER
EXEC sp_dbcmptlevel 'playdb', 80
ALTER DATABASE SET MULTI_USER

How long does this process take; are we talking seconds, minutes, hours? I imagine it's seconds, but I pose this question because a colleague reckons it will take longer because of the database size. I argue that because it's a db configuration setting, it will make no difference...

Thanks a bunch,
George