The reports I've seen range from improved performance (read/write, as well as battery life), and early death as mentioned above. If you're going to do it, I would suggest getting a good name brand (good is really a matter of opinion and past experience with flash memory, personally I have never had problems with SanDisk), and not storing anything critical.
The microdrives are nice and reliable, but the spin up and seek times are always painfully apparent when loading larger applications. If I was looking to do this upgrade, depending on the cost difference, I would get the fastest possible. Worst come to worst, the Z doesn't operate at the memory's full capability, and you use it for something else later on.
Make sure to report back on your progress.
