Some things to know...
The "mobile" sites are built for those so-called non-"web-ready" mobile browsers (Safari and Opera mini/mobile and other zooming browsers are full-web browsable), and since you never know which kind of mobile or PDA is going to try to visit the site, if you're big like Amazon you've prolly gotta have a mobile version.
Mobiles are often either touch-screen or use a stylus. Things to keep in mind then are, don't rely on hover or focus to do stuff (styluses and fingers don't seem to be able to invoke hover and sometimes also not focus). Dropdown menus come to mind. Select dropdowns (combi boxes) in forms may also be a problem (I'm not sure about this).
JS, even when enabled, drains batteries fast. As far as I'm concerned, until battery technology is improved for all popular mobiles, make the server do all the work.
Some mobiles accept a handheld stylesheet as the sole stylesheet. Some incorporate the handheld stylesheet with the regular screen one. Others ignore it entirely. I consider this a Browser War thing and would either only write for one particular mobile browser (or one that understands @media-query stuff) or sit it out. Who wants to go back to the days of "works either on Nutscrape or IE"? Forcfully steering a mobile to another, mobile-only site gets more attractive then.
Heh, Facebook sends the Konqueror DESKTOP browser to a wap page. So be careful with scripts that check OS or user-agent.
You may be able to ignore a lot of these issues if you are specifically building for one particular mobile, because then you will know the browser and prolly most of the devices running that one browser (you said you've got an iTouch). But a site working well on one mobile may not work at all on another because they range so differently.
Don't forget this isn't just phones. A friend of ours, before going to Afghanistan, bought a mini PlayStation 2 or 3 (I don't keep track of these things, whatever was available in 2008) and it used a proprietary browser which reflected a FF2 bug (but did not react to the FF2 bug fix with the -moz property) made by a company called "Oregan" I think. I could not find any information about their browser other than their propaganda (no specs). You'll run up against this, and there's little you can do. You simply can't buy 100 different phones and get a site working brilliantly in all of them.
Jamesicus once presented an interesting way to do a test among mobiles: go to a mobile phone shop, and ask the salespeople to show you how well their various phones deal with the Internet (and specifically your site, as if you would only consider buying the phone who can show your site). Sounds like something you can only do once, but it's an idea.
Interestingly, Opera's browsers are gaining huge popularity in SouthEast Asia and India. If you know your site is targetting that part of the world, you might also be able to get away with just Mini/Mobile Opera testing.
*edit I should add this: I am not a mobile user. I had one once, used it little, and now it's dead in a drawer. I have a mobile allergy. This may colour my above statements : )