"Five" seems to be a big number these days - is it compression to have a "top-5" instead of a "top-ten"? :) Over at Network world they've posted a quick slide deck of "Five things we love about SQL Server R2". They even include...the Start Menu? OK - I guess everyone has different likes and dislikes. I think they're happy that we gave SQL Server 2008 R2 it's own menu area, rather than lumping it in with SQL Server 2008 (you're welcome).
I agree with their first four for sure - and I'll throw in there things that you might not see as often, like being able to connect to SQL Azure from SQL Server Management Studio, increased database sizes in SQL Server Express, just to name a couple. By the way - if you haven't rushed over to check out the resources we have for you to learn the tech for SQL Server 2008 R2, what are you waiting for? They're free! Enjoy.
We're still using SQL Server 2005 which works Ok, so for now we have no need to upgrade. Or do we?
That's a good question - there's never a reason "just to upgrade". You should carefully evaluate what your needs are, both present and future, and plan accordingly. You may be missing some opportunities to leverage your data better.
Most of my clients are not planning to switch to R2 for years. Actually, I would say that most importnat reason for them to switch from 2000 to 2005 was that MS released 2008. Unfortunately, R2 was not called 2010, so they do not feel inclined to upgrade to 2008.