> It's slow - it scans up a class tree.

... my favorite part of the slowness is that isKindOf: causes an 
unending sequence of megamorphic message sends which routinely need 
expensive lookups or large, much more complicated caches than "simple" 
PICs so the process is not overly slow.  And of course, since the 
isKindOf: code tends to be well refactored, there is effectively one 
send site for every one of those megamorphic messages in the whole 
image, which _ensures_ those send sites will be slow... ;).

Andres.