I'm currently trying to find the best route to "easily" develop websites that work great on the following plateforms : MAC/PC (IE6+, FF3+, Chrome, Safari, Opera), iOs/Android (all existing mobile browsers) 

Most importantly, I want to avoid separating the mobile version from the rest.
I want to achieve a good looking website that uses the same HTML5, CSS3 and Javascript for all platforms.

Concerning the HTML5/CSS3 part, I'm very happy with the result.
The tough part comes from the Javascript.

At first sight, jQueryMobile seemed to be the best option for such a job.

But I noticed several drawbacks : 
- just adding the library makes fonts look kind of "blocky" on non-mobile platforms
- I'm not too fond of using their GUI
- the library lacks useful functions (ie: detection of elements leaving/entering the viewport)

As I said, I prefer to take care of the GUI myself with robust HTML5/CSS3 code.
For the viewport manipulation, I've found <http://www.appelsiini.net/projects/viewport> but it doesn't work on my Android phone and I'm unable to test my own javascript code on all platforms anyway.

So, do you guys know tools that would help me outpout custom made javascript that would run flawlessly on every mobile plateform?

Thanks in advance for your help :)