It's hard to find numbers on it, but the best I can find call it around 850k as of mid September. The Pre was released in Europe this last week, and they are "expecting" to sell another 750k or so worldwide in the first quarter of the fiscal year (Oct through Dec). That doesn't include Pixi sales, which I think are going to be pretty decent - it's a cheaper handset being marketed at the Centro crowd, which sold beyond most people expectations. It goes on sale in less than a month supposedly.
Add that to Verizon getting the Pre in early 2010 and I think by the Pre's 1st birthday we'll see 3+ million webOS handsets out there. As long as the app catalog gets some decent developers on board I think Palm will make it by and do pretty well all said and done.
The iPhone, at launch was definitely aimed at the RAZR et al more than the WinMo or RIM. There was no apps, no Exchange integration, etc. It was clearly not meant to be a business phone, and without apps it wasn't really a "smartphone". It has a good browser and it combined your trendy phone (RAZR) and your iPod. It grew into THE smartphone after a year, though.
webOS is Palm's last gasp, though. Even if they end up having to cut way, way back I think they could survive as a software company. webOS is Linux based and the apps are not compiled, they're HTML/CSS/JS based. You could compile the system onto any hardware, within reason, and the apps would still just work regardless. So, even if the Pre/Pixi don't make it, I could see them licensing the OS out to handset makers like Moto, HTC, etc.
That's one reason I think they went with the HTML/CSS/JS SDK... completely platform agnostic so they have lots of options looking forward.