With mturk, you have work you want to get done, and people go look through the HITs for things that fit their abilities.
With fiverr, you have money you want to spend, and you go looking through things people imagine someone might want to pay them to do.
I've used mechanical turk for annotating a training set for automated classification. I cannot imagine what I would use this service for. Claiming this is what mturk should have been assumes that mturk sucks because all the tasks people want to get done are boring.
I'm already hooked...
Fiverr's quirkyness reminds me a bit of http://highdeas.com/
(OT: my favourite highdea was this: http://highdeas.com/technology/Microwave_equivalent_cooling_...)
I can recommend the service, but you really should know what you are paying for , it may have some Value if you really know what you are doing and you could have a lot from $5 , if you're lucky.
"I will plant a tree in my backyard for $5"
Thanks, but no thanks.