Yes, I'm loyal to one shop, albeit not exclusive. I will shop other places if my LDS doesn't carry/can't get/is way high on price.
In all fairness, I'm working towards my Divemaster with this shop, so I do have additional forces at work. While working as a DM for them, I am representing the shop and am required to use brands/equipment the shop carries. Yes, I have bought some of it other places, or bought used.
I also buy other stuff, small stuff like O-rings in relative bulk through sites like divegearexpress.com; some of my smaller accessories come from the internet as well, but my big stuff, my BCD, regulators, fins, come from my LDS. MI can get my wetsuits from LeisurePro for less than my LDS can buy them, so it's a no brainer.
I'm personal friends with 90% of the staff and if I'm going to the quarry and not working with one of their classes, I'll set up right next to them so we can socialize after the day is done. I travel with the shop as well, both locally on weekend charters as well as trips that are a flight away. However, I'll book a trip or a weekend charter without them; like I said, I'm not exclusive to the shop.
Most of my training is through them too, but there are a few courses that while they DO teach, they're not experts in, such as Sidemount; I'll go to an outside instructor who dives SM every time they dive. Like I said, I'm loyal, but I'm not exclusive.
Long story short, I'd rather give this shop my money; they've been great to me. The people are great, the selection is great, the atmosphere is great. However, if I can't get it, can't get it fast enough, or can't get it cheap enough, I will do what's best for me. I'd say 80-85% of my business goes through them without a second thought, but I'll go elsewhere if I have to.