Our company is considering upgrading our SQL server.
At this point, would it be better to upgrade to 2005 or 2008?
Here are some of my considerations:
Bear in mind our staff has already been using SQL server 2000 for many years.
2005 is already quite different from 2000, at least in best practices, as a number of things like error handling are greatly improved. As far as learning curve is concerned, if you're going to throw the learning curveball at them anyway, they're probably better off learning the new technology rather than the one that is already a few years old.
Beyond that though, it's difficult to comment on new features without you providing any info on what kind of work your company does. One thing I'm very excited about in SQL 2008 is the geospatial data type that I wish had come out a few months prior (perhaps, the initial planned release date) as they would have made our huge mapping application much easier...
I would go straight to 2008, since there are already enough differences that you need to fully re-test your software against 2005 or 2008.
If you're porting your SQL Server 2000 codebase to SQL Server 2005 or 2008 the effort to go to 2008 is not going to be significantly greater. While 2008 has some features over 2005 the difference is not so great as the jump from 2000 to 2005. I would suggest going straight to SQL Server 2008 with the following major pros and cons to the decision:
Pros of going to 2008
You get another 3 years of lifespan for your systems essentially for free. SQL Server 2008 will be in support for longer than SQL Server 2005. This gives you a longer stretch before you will have to mover over to the new version. IMO this is probably the strongest argument for going straight to SQL Server 2008.
You get some features such as geospatial indexing that are not available in SQL Server 2005. While your SQL Server 2000 applications will not use these features initially, you get more options in future without having to do another platform shift. For your porting exercise this doesn't matter but you buy yourself a little flexibility nearly for free.
Pros of going to SQL Server 2005
It's less 'bleeding edge' than SQL Server 2008 so the implementation path will probably be slightly easier.
Recruiting people skilled with SQL Server 2005 will be easier than getting experienced SQL Server 2008 people. However, presumably you will mainly be re-training your existing staff so this is not likely to be a major issue.
YMMV on some of these points, so you may wish to do some more detailed investigation about the potential issues and see if there are any real benefits or obstacles that are specific to your circumstances.
I would choose 2008, without a doubt.
Have a look at new features of MS SQL Server 2008 - some of them are great. What I find the most importand is performance. In my scenario SQL2008 performs better.