I think the jury is still out on that one, princess.
One might ask, what kind of site do you have?
Mine is a directory/portal, of sorts. Purely altruisitic mind you, but considered a directory/portal nonetheless. I have roughly 5,000 outbound links and enough quality inbounds to keep me at PR6.
Once I've listed a site I go back six, maybe seven months later and 'submit my site' (e-mail has my URL and sig in it). Normally, once they've seen the magnitude of my domain, the inclusionary request is immediate.
That still leaves your question: How?
Write 'em a short, concise request for inclusion without the mention of reciprocity as it eliminates all PR associative pressures, allowing your request to be considered on it's own merits. Me thinks me does better thatta way :) Naturally, your site may not hold to this value.
Also, the least amount of 'Links' a site has, the better your chances are of becoming listed with them.
Many webmasters could care less about PR, although not those who walk the halls here at WebmasterWorld. To those who garner income - life beginning and ending w/PR is quite understandable.
Forget (for the moment) whatever benefits PR may seem to bring you and devote your time to meticulously and individually adding your site to those who share a commonality with yours.
That's the way I see it....