www thing IS an issue, as the search engines will only choose one (either with it or without it) to list. so yes, you should definitely be as dilligent as possible with that.
but that's the only part of your URL that might cause you any pain. otherwise, as i said, the "deep linking" is a GOOD thing.
if anything? the fact that all your pages of comments are going to have essentially the same content (with the exception of the comments) might give you trouble, because essentially you're telling the search engines that pages A, B, and C all say the same thing. not too good, honestly.
especially if you wind up with
and so on, where the only change in content might be your comments. it's akin to creating a site with 100 pages of content that's all the same, but only changing the last few paragraphs.
i've been along the ride with you while you were trying to figure out how to do this, and while it's not my business (here in the forums, that is) to ask "why?" - it doesn't make much sense to me why you'd really want to do this in such a way... if anything's going to hinder your SEO aspirations, it's this setup you've chosen.
and yes, it did kind of sound like you assumed i had no idea what i was talking about with SEO - thanks for the clarification. part of the problem with "DIY SEO" is that you find yourself listening to 30 different people who do things 130 different ways sometimes, and it's easy to get confused. but i wanted to let you know that i've had a great success rate over the last 6 years, and to understand that i have no reason to steer you wrong. in a way, SEO as a "skill" has gone the way of web design, where anyone with a computer and frontpage can try to call themselves a web designer, but there's a difference between someone who can do it, and one who can do it exceptionally well... ;) just be careful who you listen to, as as far as i've seen, no one out there has been able to keep up with the search engines enough to write a bible about SEO that makes sense 15 minutes after it's published... SEO is an ever changing field, and sometimes people refuse to change with it, but still offer the same old advice they always have, and they're often wrong.