The SQL Server Customer Advisory Team has a great blog and they have a good article here about upgrading to 2008. Lot of reasons to upgrade to 2008 (especially if you are on SQL Server 2000 or earlier). Check it out; http://blogs.msdn.com/sqlcat/archive/2008/12/08/ultimate-guide-to-upgrading-to-sql-server-2008.aspx
Article by Mike Walsh
Mike loves mentoring clients on the right Systems or High Availability architectures because he enjoys those lightbulb moments and loves watching the right design and setup come together for a client. He loves the architecture talks about the cloud - and he's enjoying building a Managed SQL Server DBA practice that is growing while maintaining values and culture.
He started Straight Path in 2010 when he decided that after over a decade working with SQL Server in various roles, it was time to try and take his experience, passion, and knowledge to help clients of all shapes and sizes. Mike is a husband, and father to four great children and lives in the middle of nowhere NH.
There are many reasons actually for upgrading.
My reasons are :
FileStream, Bakcup compression, and especially change data capture
I required this feature a lot in an application.
So if I was working with the new version, things will be far more easier