Kent Pribbernow of PocketFactory gave a severe tongue-lashing to palmOne and palmSource in his editorial, The Sad State Of The Palm Economy, And Other PDA Ramblings. He argues that most of the current palmOne PDAs are poor competitors to Pocket PCs at the same price points. The Treo 650 is spared much of this criticism, since many analysts agree that it's the leading smartphone at the moment.
I'm focused entirely on the Treo 650 at the moment, since business has firmed up to a point now where I'm finally able to plan the purchase of a replacement for my late lamented Treo 180. A lot of the palmOne PDAs I've looked at recently (like the Tungsten T5) are hard for me to imagine using on a day-to-day basis.
I think the issue that Kent Pribbernow raises about the uneven quality of third party applications written for the PalmOS is an excellent observation. A lot of these programs are simply not well supported-- probably because developers often dosn't profit sufficiently from maintaining Palm OS software. Some of the most popular third-party apps are maintained on a shoestring and written to the lowest-common-denominator of PDA functionality.