I posted this as a part of the above thread. It may be deleted, Apple's policy allows them to delete commentary of this sort.
... Thanks for the warning! I've also read that iPhoto 5 does not work fully on older machines (G3 iBooks) -- many of the new editing features require a G4 (or perhaps use a newer GPU?)
You will receive many replies to your post essentially "blaming the user" for not running UNIX maintenance scripts, not running one disk repair utility or another, not repairing permissions (that's largely superstition by the way), not deleting caches, not forcing iPhoto database restores, etc. Some of these posts are somewhat accurate, but all are irrelevant to the main point -- OS X is marketed as a consumer OS, not a geek platform. (Ironically, some versions of classic had more problems than most OS X releases -- so it's not the 'UNIX' underpinnings that cause issues.)
I believe Apple doesn't do enough beta testing. They ought to have released iPhoto 5 in a public beta, as Google does with their apps (Gmail, etc). Of course this is contrary to Jobs passion for secrecy and big bang product launches. Jobs is a genius, but his interests are not the same as ours.
The RAW support in iPhoto is weak. They shouldn't have gone this route -- the manufacturers simply aren't willing to cooperate. Adobe has spent a fortune reverse engineering RAW file formats, that's why they're championing a "generic" RAW-like file format.
As to the import problems you ran into, similar experiences were seen with iPhoto 2 to iPhoto 4. At that time it seems iPhoto 2 had some severe bugs (they may have been in OS X, we don't know) that led to corruption of the iPhoto 2 database; this corruption was often invisible to the user. The initial release of iPhoto 4 responded to the problem badly. Later iPhoto 4 releases seem to have managed iPhoto 2 database corruption better.
It may also be that you have a hardware issue. Do you use an external drive? External firewire drives have often been problematic with OS X, especially with suboptimal cables. The iPhoto 5 update is a severe stressor on drive i/o, it might precipitate i/o errors and lead to database corruption -- even on a journaled file system. (This might be especially true if you had your iPhoto Library on an external firewire drive that was not journaled.)
Finally, I do want to affirm that I (at least) agree with you that consumer software is far, far from what it should be. Apple is not alone, I do most of my work on XP and Microsoft is at least as guilty. (Apple has very demanding customers, that helps. Microsoft customers have largely learned helplessness.) Perhaps the newer NetApps from Google will take us down a better path. In the meantime, backup relentlessly (yes, backup is FAR more costly, difficult and less reliable than it should be) and, above all, don't install anything until it's been on the market for at least 2 months. Sad advice indeed, but true.