GG answers several questions from a newbie. The answer to #6 is the most interesting in which he gives examples of link-types that may not count at all towards PageRank.
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Good questions! I'll tackle what I know:
1. I believe if you've only been in DMOZ for about a month, it's just that we haven't updated our directory recently enough to pick you up.
2. It's possible. I would be aware if the pages that you're linking to look spammy to you. But PR0 can also be because it's a new site or because there aren't that many links to a site, so I wouldn't worry about it too much if the pages seem fine to you.
3. Higher PageRank increases the chance of being crawled/indexed/cached. If we're crawling you each day, I wouldn't worry too much about what the PR bar says.
4. If you want to be safe, I'd feel free to do a reinclusion request by emailing webmaster [at] google.com with the subject line of "reinclusion request" and describing what you think might have affected things (e.g. if you see on archive.org that the domain looked spammy before it expired, or your webmaster put anything bad on the site like doorway pages, hidden text, sneaky redirects, etc).
5. reinclusion requests get batched up, so they can take a little time to get processed, but I do think it's worth if if your domain might have had problems in the past.
6. PR0 can be a penalty, but the vast majority of the time it's because a site is new, or there aren't that many links to a site, or there are a lot of links to a site but they're of lower quality and just don't count for much or any weight at all (machine-generated links, or guestbook links, or blog comment links, or links to a domain from before it expired, etc. etc.). If a site owner is looking to take shortcuts to get free or better link popularity, they shouldn't be too surprised if the shortcut that they hoped would help them doesn't really help much or at all, or if it helps for a short time but those links count for less over time. That doesn't sounds like that's the case with your site, but just thought I'd mention it.