Fellow MVP Aaron Bertrand has blogged about the MRU (Most Recently Used) server list in SSMS under SQL Server 2008 and how hard (and unsupported) it is to clean it up versus how it was under SQL Server 2005. Please give that a read and head over to Connect to vote for his suggestion as you see fit.

(it’s easy [but still undocumented] under SQL Server 2005 – just delete the mru.dat file…)

Connect item: https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=424800