Treonauts has a nice comparison of the web browsing experience with Blazer (the built-in Treo web browser from palmOne) and Xiino (from Mobirus). Their overall conclusion showed Xiino being significantly faster than Blazer. I’ve heard good things about Blazer 4.0, but for now it’s only available on the Treo 650, not as a separate software package.
Checking back on my analysis of mobile user agents, I do show a very small number of Xiino hits (only 0.22% of the total).