I've had the 160gb every since Tiger came out (I remember ordering them at the same time), so April, which makes 9 months.
The 250gb I've had for about a week, so too early to tell if it will encounter any serious problems.
I, for one, wasn't attracted to purchasing an internal drive and an enclosure. I like the all-in-one form factor of the Porsche's. They look and functions perfectly.
From what I can tell, the drives are of excellent build quality. Until something happens, I will surely keep buying them. If you have any qualms, you can always purchase an extended warranty.
I know I kind of rambled, but I hope that that helps somewhat.