Arthur Worth, the chap who first taught me beekeeping did not favour landing
boards for the very reason that Tom likes them.  His reasoning was that the
bees that don't make it back into the hive are bees that are on their last
legs (wings?) through age or disease and the hive is better off without them.
It might be an interesting project for a student to gather up a sample of the
bees that don't make it and compare it with a sample of the bees that do.  We
may then be able to base opinions on fact rather than anecdote.
Chris Slade