ID tags are used in tables to assign them to variables when used in forms, code, scripts, etc or to label them for ease of use. They are not a form of infomation like the "title" tag or "alt" tag or "keyword" tag or "description" tag.
In response to Doug's reply, these tags are hidden on the page for a reason and are extremely useful to google, yahoo, msn, and every other search engine that uses standardized HTML indexing.
Google will not take information from places they know aren't used for information and cache them in your favor. Google will simply overlook it. You can put what you want in there, it won't do anything at all. Just like all that javascript, doesn't do anything at all except add load time to the page.
The tags on the page you need to be focusing on are:
1) <a title="" href=""> - the title tag on href links or hyperlinks. It will drop down that little window that images do showing you that title. This is used to show what the link is for if you can't read it for the visually impaired. If you have your computer set right, those tags are read by the voice assistant on windows to that person. Obviously these are good for keywords about your link or page that is to follow.
2) <img alt="" src=""> - the "alt" tag on an image is used to show people what the image means if they can't see it, visually impaired or browser settings.
That's really all you can do, except put those links and images all over the page. Remember to mix it up, not all the same keywords.
I would have to politely disagree with Doug, I have several sites with very extensive ID tags for security and they have no bearing on the cached content from those pages.