I used to buy disks with more plates but I stopped doing that as it seemed the more plates the shorter the live of the disk.
4 plate disks are about as many as you can put in the form factor, however I have seen a competitor put 5 plates in a drive. I cannot speculate on how long it lasted.
Today most of my disks are 2 plate (4 head) disk assemblies. These seems to be reliable. I wonder if 3 plate models are now joining the 4 plate disks in the graveyard?
Of course cheaper models may have a single plate. I dislike that practice as it tends to be more of a disservice to the end user down the road. 2 plates are better as there is lots of storage.
My netbook came with a 160 GB disk but I replaced it with the WD3200BEVT I purchased as new previously. The disk was in a USB case when I bought the netbook.
2 plate disks are fine for the desktop and the portable.