Thanks for your response, Jimmy. Very helpful.

At this time, I don't need to utilize mobile-specific API so native apps would be a low priority.

I can see how I might need to design HTML5 layouts for different sizes (desktop, tablet and mobile).

I hestitate to deal with different browser implementations of HTML5. I might take the "lowest common denominator" approach to design. In other words, use the features of HTML5 that are common in all of the major browsers.

Would be nice to have a tool that helps me design for different layout sizes (desktop, table and mobile, etc).

I really like what you've done with ClientUI and the way that accessibility is baked in. That's really excellent. If Silverlight was the future for public websites, ClientUI would've been my first choice. If I was developing internal line of business websites, then ClientUI is an excellent choice. But since I'm developing for a public website, ClientUI/Silverlight was my first choice until Microsoft's message on Silverlight started to get muddled, especially when no plugins will be allowed in Windows 8, which includes not allowing Silverlight unless I've misunderstood).

If and when you do create a tool for HTML5, please bake in accessibility. It's the right thing to do.

Any suggestions on capturing UX/UI actions for support and usability statistics?