I think it's still the case that someone who demonstrates knowledge of
the background material and understanding of how the Internet works is
quite welcome at IETF. Clueful people are in short supply, it's usually
quite easy to distinguish them from less clueful people, and clueful
folks that show a willingness to contribute seem to get the opportunity
to do so quite quickly.
Having said that, I will observe that the most effective path to making
useful contributions in IETF meetings seems to be to first make useful
contributions to a WG mailing list. Folks who aren't actively participating
in at least one WG mailing list should probably think twice before
attending an IETF meeting. (however there are other reasons - such as
relevant BOFs - which might justify attendance anyway)
Keith