In my local server, before my buds stopped playing minecraft, we had amassed a total of around 64 diamond blocks and a bit of change, nearly half a stack of additional diamonds. So... around 600 or so, give or take?
Granted, that was with around a month of playing in that one world and a very, *very* extensive mining system.
I would have to say my hardcore Ender dragon run world was probably the most I've ever gotten. I got a little more than two stacks of diamonds and that was without any fortune enchants.
Some worlds have a lot when it comes to finding diamonds. In others, you may not be so lucky.
Distribution wise there should be the same amount of diamonds generated per chunk in every world. Its the other things that are generated after the initial terrain generation like abandoned mines, chasms, dirt and gravel pockets, water and lava pools, strongholds and caves that can replace diamond nodes thus reducing diamond ore numbers in some areas.
688 in the time i've been playing that world (must have been 60-90 days)Total? 2012. I never mined another diamond after that, apart from the fact that i have 50-60 worlds :PPPPive had the game for 1 and a half years now. Got it when the game just hopped into beta.
Umm...I'm new, and i pretty much suck at Minecraft, the most i've found is 10 diamonds in my current survival world. My diamond pickaxe doesnt have any enchantments as of right now, since I'm waiting for 1.3 to come out with the lowered enchanting levels.