SQL 2008 VS. SQL 2005

Arguably the most potent tool for DBA's in 2008 would be Policy Based Management. Tom LaRock did a nice 3-video walk-through with Brent Ozar which you should probably check out:

http://tomlarock.com/?s=policy+based+management

I also cover PBM in my blog/talks/presentations

http://sqlchicken.com/category/policy-based-management/

My PBM fanboy-ism aside, here's the list to all the new features available in SQL 2008

http://www.microsoft.com/sqlserver/2008/en/us/whats-new.aspx

Well, I've used the Date & Time datatypes, compound operators ( @i += 1 ), GROUPING SETS, MERGE, Row constructors and the enhanced Declare.

For me, the single most important enhancement is the sys.sql_expression_dependencies system view - at last a dependencies view that isn't broken.

A close second comes filtered indexes - but really SQL Server is on catch up in that arena with regard to other DBMSs.

I think some of the best features in SQL2008 is Date datatype (no more conversions to strip the time), Data compression (requires less IO operations) and filtered indexes.

I activated PAGE compression in one of our databases and reduced the size from about 1 Tb to 400Gb and increased the performance due to less IO. Data compression uses more CPU, but we are using a server with 4 quad processors and 64Gb memory. :)

With filtered indexes i can create more covering indexes with increased read performance with only slight write overhead. Covering indexes reduces Key lookups.

The enhancements to SSMS2008 over SSMS2005 are fairly significant, I especially like adding missing index information to execution plans and the addition of intellisense. The ability to query multiple servers at once is very useful in some limited situations. http://www.sqlservercentral.com/articles/Management+Studio/63536/ provides an introduction to some of the SSMS enhancements.

Also, small tweaks to TSQL such as the ability to initialize a variable when it is declared are nice in a readability sense.