List all keywords?

Hi,
I need a shove in the right direction. Rather than create a category each time I need some new taxonomy edge for a post, I’d like to simply add a “keyword” field to each new post. Then in my template I’d have some code that looks through all the posts for “keyword” fields and makes a list of all the values, with each item linking to a list of the posts that use that value. Sort of like the Searchwords thingy described at Gadgetopia (http://ww.wp.xz.cn/support/10/2468) but extended to allow the blog-wide list. It would be sort of like a free-form category field.
Any ideas on how I’d go about implementing this? I know I could just do some SQL, but I was hoping someone had done this already.