The problem is not their hardware. The hardware is great. It's their inability to deliver on a stable, usable operating system. Whoever has been in charge of the OS division of their company should not only be fired, but charged with criminal negligence.
They haven't yet delivered on their Linux OS, and their use of Microsoft Mobile is a total disaster.
In my own experience, I've owned several Treos, and recently upgraded to a 750. It came with Microsoft Windows Mobile, which, though I generally haven't had good experiences with Microsoft software, I thought I'd give a quick whirl. Little did I know what I was in for.
Among the many, many instabilities, the worst is the SMS application. It freezes about 25% of the time when a message is received, dropping the message. This means that SMS is basically unusable. Perhaps an upgrade would fix it, but I hesitate to upgrade because the online message boards are filled with posts of people who've attempted the process and bricked their phones.
I was also shocked to discover that there's no way of syncing your calendar, contacts, etc. on Windows Mobile without using Outlook. No way at all, unless you want to rely on a really buggy pre-alpha open source package, which I don't.
I don't like Outlook, I don't want to use Outlook, and I certainly don't want to pay for more Microsoft software after I've already (implicitly) paid for their OS, which replaces what Palm previously did for free.
I've given up on waiting for Palm to get their act together. I still love their hardware, but their total incompetence in delivering a stable and modern OS will mean I, for one, will never be a customer again.