Why do you want to shrink? Databases tend to grow as more data gets put in them. It's in their nature.
Shrinking causes massive fragmentation and will just result in the data file growing again next time data gets added. When that happens, the entire system will slow down as the file is expanded. Also repeated shrinks and grows will cause fragmentation at the file-system level, which is hard to fix.
See - http://sqlinthewild.co.za/index.php/2007/09/08/shrinking-databases/
Shrinking won't make your backups any faster, because backups only read allocated extents, not empty space.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability