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Yes, we try not to crawl garbage directories, no matter how large they are. Check out Dr Pete's post, Where's The Love, DMOZ?, where he talks about how a lot of the large directories that are spammy (or even ones that aren't) aren't index by either OSE or Google, especially as the categories get more finite. We currently don't have a place to suggest sites. However, you can head here to vote up the suggest feature for a place to submit/suggest sites for indexing.