Don’t name your stored procedures with sp_
I found the following note:
Note: Do not preface your stored procedure names with sp_, because doing so reduces performance. When you call a stored procedure that starts with sp_, SQL Server always checks the master database first, even if the stored procedure is qualified with the database name:
at this URL: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnbda/html/BOAGag.asp