skjoldtc makes a good point. Having a blanket policy on which version thorughout the organisation isn't good. If an application can deliver better ROI by upgrading then it's winner.
There are some very compelling reasons to upgrade to SQL Server 2008. I'll cover a few here but haven't got a huge amount of time so apologies for appearing curt:
If only everybody followed a naming convention. Generally this type of discussion sparks a lot of passion since we all have our own style. Essentially...