I come from a little different angle though – I have spent too many hours trying to figure out whether problems I am incurring are due to jQuery bugs or my own misunderstanding. I’m more of a server-side programmer anyway and this stuff drives me nuts when I can’t even write sample code to figure out what is happening.

Straight coding does not take more time when you are spending half your time with a framework trying to figure out why it is doing what it is doing.

You get caching for free, it’s called “variables”

exactly!

You may argue that getElementById is probably faster if you need to get elements by their ID, but do not confuse optimization with over-optimization. How many elements could a mobile page have? Plus, you should really cache the elements you are going to use in your code, so you are not probably querying DOM 30 times per second

Why are you implying that you need a framework to cache your DOM query? Because you have a hardon for using $? You get caching for free, it’s called “variables”

Isn’t the right way to include jQuery to tap into the Google repository?

It doesn’t matter. The newest stats (2010) I can find on browsers for mobile devices have a cache limit of 4MB. JQuery by itself is 24KB (minified+gzipped). The odds of keeping this in your cache is pretty small when you consider all of the other assets you’ll be downloading on any given page (CSS, images, other JS files, the page itself).