"Useful" -- "useless" are global concepts, but the reality is personal. What _I_ use (repeatedly) may not be what _you'd_ EVER use (and vice versa). Statistically, it is absolutely true that for MOST people, suggesting a site is "useless" -- it's not something they'd gain benefit from doing repeatedly. Think about it.
-- Most surfers don't hunt up lots of sites to suggest.
-- Most people who have an honest website, have one website, and once they suggest it once, they've extracted all the use from the ODP that there is.
-- And who's left? a TINY handful of professional web developers who create sites for other people who own their own businesses but don't want to build their own website: these people MIGHT suggest each website they build, on behalf of the business owner who commissioned it. For this tiny group, the ODP might conceivably be "useful".
--Oh, yes, then there are the large number of affiliate/doorway spammers who constantly churn out new ad-banner-farm sites, but who cannot and will not EVER create even ONE listable site. These are the same folk who fill the net's SEO blogs and forums with babble about what serves their exclusively-greedily-mercenary self-interest. (Hint: the ODP doesn't serve them. And that's a good thing for every honest person.)
So I'm not inclined to worry too much about whether any particular person finds any particular website "useful" or not. I use what benefits me, and that's less than one in a million of the world's websites. Every other surfer uses what benefits him, and ... that's a DIFFERENT one of each million websites. If I find craigslist useless (and I do) I don't visit it. No criticism of either me or Craig is involved. If you find Project Gutenberg useless, that doesn't say anything (good or bad) about either you or Michael.
So why would the ODP be any different? Some people like to build it, some people find it useful. And everyone else ... has another 100 million sites to try to find some use in.