i am a sql developer and i use sql 2005. i want to now to pass to 2008 but i am a little affraid. can anyone gives me some advices about this. should i still continue using sql 2005 or is better pass all my projects to 2008 due to better performace?
Who is going to use your projects; if they are going to customers with existing SQL Licenses then 2005 might be the way to go; assuming they are running 2005. SQL 2005 databases will work on 2008; though if you use some of the new language features in 2008 then the SQL2008 databases wont be backwards compatible to 2005.
If you are controlling where they are going to be deployed; some of the new features in sql 2008 might be of interest; better full text search, improved Analysis services, reporting services and some language tweaks. If you are managing the servers; your admins will likely appreciate the new management features in 2008.
I moved 6 projects from 2005 to 2008 without any problems except reporting services. To me the biggest benefit is the SQL Management Studio enhancements like auto complete and change history.
The only reason I did upgrade was because I work in education and Microsoft is very gracious on licensing.
In general, unless you hear that it is a disaster, I think you should strive to use the most recent release at the earliest opportunity. The advances in server functionality and the tool set will usually offset the time it takes you to learn the new features. All software is built with planned obsolescence in mind, so you will eventually need to migrate to newer technology. If you make a habit of migrating your systems to the latest technology, you will find that the migrations become relatively painless.
I moved to 2008 because I am heavy into SSIS and have large databases meaning: The backup compression and increased concurrent processes in SSIS for 2008 make it worth it for me.
One of the benefits of SQLServer 2008 with respect to SSIS is that it includes very fast bulk connectors for Oracle and Teradata (well, the development and enterprise versions do).
So if you need to move data between SQLServer 2008 and those databases you get this for no additional cost.
See Microsoft Connectors for Oracle and Teradata by Attunity
Another major benefit in SQLServer 2008 is the new Change Data Capture (CDC) functionality which means you can build your application in any way you like and then if at later time you are interested in starting some processing when table X changed, you can turn on CDC for that table and get a change table that contains all the changes to table X with minimal overhead. Ben Hall did a useful post on this.