Features in 2005 that work in Compatibility Mode 80

[eavery@cdc.gov]

Is there any documentation on the new features that do/don't work when
you set the backward compatibility for Sql Server 2005 to 80? I tried
the online index rebuilds and it works....but I need to know how much
we are giving up by not using the full features. Developers are
reluctant to modify "working" code to work w/2005.