I wish I got tipped!

As a DM who only works classes, I can't tell you the number of times I've spent tons of one-on-one time with a student, working on whatever they're having problems with, going over tables with them because they were afraid to talk to the instructor after they'd already told them they understood it, helped them with their gear, run and gotten them extra weights from my car, leant them my extra personal gear for a class, and God knows what else! Never seen a tip yet - hell, never seen an offer of buying me dinner or even a drink yet!!!
I totally disagree with people who say that DMs get into this for "the experience" - BULL! I got into DMing so earn some money for a couple of years before going on to instructor. My shop pays per class...so it never occurred to me that I'd actually LOSE money on every single class I accepted between the price of my liability insurance, my cert and the gas it takes to drive back and forth to the dive site and the pool. Yes, I still love it, and I'll continue to do it, but that's only for as long as I can still take the tax deduction showing the financial bath I take doing as a DM ever year. When I can't take that tax loss anymore, I'll say to hell with it and finally make the leap to instructor... so I at least stand a *remote* chance of breaking even - something that will *never* happen as a DM.
If you get great, personal service that goes the extra mile from an instructor or a DM, it shouldn't matter if it's in a learning setting in my opinion...yes, a tip would be appreciated as an expression of your thanks.
As far as tips on a boat setting go from certified divers on vacation, I do agree that in countries where tipping is the custom, tips are *not* optional - they are part of the cost of diving. If you can't afford to tip, then don't dive until you've saved up enough money to adequately tip. The boat crews work hard and deserve to be recognized for their hard work making your trip enjoyable (assuming they've done so) by a tip. Diving is an expensive sport and if you can't afford a tip, you can't afford to go diving that day. Look - I'm FAR from rich, but I make sure that when I dive from a boat, I have enough money to show my appreciation for service that could be well above average - that way if it's just average, I have enough, too.