I've got direct-fibre IBM LTO-2s and I can confirm that they definitely
will require cleaning at some point.  A good indicator would be when the
big red C lights up on the front of the tape drive :)  Seriously though,
they don't require cleaning very often.

One thing I've come across lately is a few LTO-2 drives which had really
poor performance (about 2-3 MB/s) and would require cleaning on a daily
basis.  The daily cleaning requirement was the first warning sign that
the drive had gone bad.  IBM replaced the drives.  

Russell