Hi Hamish,
The table wiki page is in the standard format for all iRule wiki pages:
http://devcentral.f5.com/wiki/default.aspx/iRules/table
And there is a link on the wiki page to the series of table articles.
http://devcentral.f5.com/Default.aspx?tabid=63&articleType=ArticleView&articleId=2375
And here's one notable section:
http://devcentral.f5.com/Default.aspx?tabid=63&articleType=ArticleView&articleId=2382
Limitations
As fantastic as the new session table is, it does have its limitations. You can't use the table command in RULE_INIT or any other global event.
There's no way to access the session table outside of tmm. The ability to count and list keys is limited to subtables. Timestamps are limited to 1-second resolution, so there's no way to do counts for sub-second events.
As you saw, you can use it for accurate counting, but that's not nearly as easy to use as we'd like it to be. We tried very hard to come up with a command, or set of commands, that would hide all the table manipulation and just do the counting for you, but everything we came up with was either very complicated or would always use the most computationally expensive method for counting, and that seemed like a bad tradeoff.
Aaron