I've only recently started playing around with SQL Server 2008 for a new project I'm working on. To date I've found it very easy to use, especially coming from SQL Server 2005. One thing that I noticed early on was my inability to edit any of my tables using design mode. Anytime I wanted to change the column to allow nulls or adjust a column type I would see this error message in SQL Server:

Saving changes is not permitted. The changes you have made require the following tables to be dropped and re-created. You have either made changes to a table that can't be re-created or enabled the option Prevent saving changes that require the table to be re-created.

To stop this message occurring all you need to do is go to Tools and Options from the SQL Server toolbar. A popup will open on screen. Simply select the Designers option from the left hand navigation within the popup window and uncheck the option that says 'Prevent saving changes that require table re-creation'. Click 'OK' and your done. If you now try to adjust your table using the table designer in SQL Server 2008 everything should work OK for you.