This script will show you how much diskspace can be reclaimed by shrinking all the logfiles of userdatabases using a DBCC SHRINKFILE(2) command.
Often the spacegain is much smaller then expected. SQL Shrinks logfiles the end of the file until it finds the active part of the logfile. (If the active part of the logfile is in the end of the file, shrinking won't reclaim any space).
usage: exec ShowSpace2BFreed
When doing bulk data changes it may be beneficial to disable indexes prior to starting the operation. Fortunately, SQL's rich metadata makes this very easy to automate in a robust fashion.