Thanks for the thoughtful comments on comm. holes,
which tend to reinforce my opinion that they
may be useful, but certainly are not necessary.
I am curious that some see holes only at the top,
and others only at the bottom.  Either there are
real differences out there in bees, (location?, race?)
or perhaps systematic differences in hive/frame
management that may produce the effect.
 
I can offer three tips to the excellent comments on
obs hives.  First, 1 1/4 plastic sink drain pipes
have nice slip type connectors, flexible sections,
etc., which do a nice job for easily undoable but
sturdy plumbing.  Second, try to have a screened
opening (a "T" connector) between the outer entrance
and the hive to equalize air pressure.  That prevents
unwanted draughts in the hive itself.
Third, "lazy susan" devices are available, which are
pressure bearings with 2 inch holes in the middle.
Their use makes it easy to put the entrance in the
middle of the bottom or top, resulting in a rotatable
hive, so viewers can easily look at both sides.
When I have used such a hive for demonstrations,
however, you have to watch out for chaps who want
to see how fast they can make it go around!
 
Installing frames with young eggs and larvae
sans queen always produces a fascinating month
of viewing (schools), as John Romanik points out.  Having
a well-marked queen is best for single visitations,
like fairs and talks, where the full queen raising
cycle cannot really be appreciated.  A simple note
like "The Queen has a [red] dot on her thorax" is
all thats needed to instigate the hunt.
IMHO (I hate that acronym!) every nature center should
have an obs. hive.  Beekeepers, lets get busy!
 
Wayne Esaias
Central Maryland.