SQL Server 2008 R2 Management Studio : "Evaluation period has expired"
You've already I assume, applied the registry fix suggested by Microsoft. 

Since they are saying that this has been resolved since SP1, have you considered installing a newer version of SQL Server 2008 R2 Express?  

http://www.microsoft.com/en-us/download/details.aspx?id=26729

Update 12:27

Based on what you're saying and without having your system in front of me, I'd try to find out if the evaluation edition you think you removed might actually still be there.  

You can run the SQL Server features discovery report to find out what components are actually installed on your laptop.

Start -> All Programs ->  SQL Server 2008 -> Configuration Tools -> SQL Server Installation Center.  Then on the left you select Tools, and then click on the Installed SQL Server features discovery report.

Installation Center - Tools



Features Report



I would also go Control Panel, Uninstall Programs, and make sure there wasn't anything left over from the evaluation edition.  Once you're absolutely sure that evaluation is gone, reboot the system just to make sure that the registry is reloaded correctly.