One always thinks that one should support the local dive stores,
because in times of need Leisure Pro is not going to fill your tanks
over the internet, etc.
After ten years of diving and buying stuff, and a recent encounter of
the strange kind at my local dive store, I am leaning heavily towards
mail order. Here is the tale of my most significant experiences:

The strange encounter happened when I stepped into Ocean Adventures on
Lincoln (LA, where I live now) and asked what I needed to make the DIN
valve of my regulator fit into the din valve of a tank I bought on
Ebay. Turns out the Ebay find is a 300 bar tank, but in addition to
that information I got the whole wrath the dive store owner has for
Leisure Pro etc., when he asked me where I had bought the regulator:
Upon hearing New York, he went into a little fit:
"Leisure Pro? That's what happens when you buy from them,
non-fitting,... blablabla, ... can't help you with that, ... blabla,..
", etc., etc., you know the song.
He didn't seem to want to go back to normal conversation mode, to
either hear that Leisure Pro was my local dive store when I lived there
(with a much larger selection and better service than his, btw.), nor
that they hadn't sold me that combo, but that the tank came from Ebay
years later, and that I was trying to by whatever part was needed from
him. So I stepped out.

The second worst experience with a dive store was a guy who serviced my
regulator, but never 'got around' to give me the paperwork for the work
done. I kept calling and sending faxes until I lost interest, because
the next service was due. That was the store in Germany where I had
bought fins at a $50 above internet to support my local dive store, and
air and small stuff. Turns out that he mailed the regulator to a
service center, anyway, hence his disinterest in chasing down the lost
papers.

The  only bad experience with mail order was Paulis Tauchshop in
Germany (http://www.paulis-tauchshop.de/), who didn't refund a return
for about a year. But this money was recovered without cost or much
effort to me through a lawyer, whom Paul paid for.

One really good mail order experience was another German store whose
name I forgot, who gave me the sales price for an item that I had
ordered even though it went on sale only a few days after I had
ordered.

The dreaded Leisure Pro turned out to be a small store cramped to the
ceiling with interesting diving stuff at great prices, a pleasure to
browse and buy. I didn't find the lack of constant PADI indoctrination
a shortcoming.

A completely different animal not to be confused with stores are dive
operators; I had mixed experiences with these. Interestingly enough the
bad ones were with operators in the united states, the really good ones
in remote parts of Europe, and Asia and Africa.

So after ten years of random sampling, the score:

Local dive stores: 2 really bad experiences (-2), generally high price
level (-1), local service and fast availability of small parts (+1):
negative two points

Mail order: One annoying experience (Pauli) (-1), one positive
experience (+1), good prices and huge selection (+1): positive one

So for me the internet comes out three points ahead. My dive store may
go the way of the dinosaur and the horse carriage, I will get pure air
without attitude at the Sports Chalet down the road or from a vending
machine at the dive site, my equipment through the UPS truck, and my
trips from able operators.

I would be interested in hearing other peoples experiences. Is this
unique, or the rule?