I'm not at all saying this is a bad thing, you're giving away a free service, just wondered if it was part of your considerations.
tbh the thought never even crossed my mind, what happened is that on the #startups channel on freenode.irc.net someone asked me if I would give them a vanity domain on ww.com so I said sure.
Then two other people asked for it, and I suggested that maybe we should offer this to HN rather than just those in the IRC channel.
The thing that has been mostly on my mind is actually the opposite.
Plenty of people are asking for domains that were in use at some point, and ww.com actually relies on a lot of those old domains and backlinks from them for its traffic.
So if anything I'll probably end up taking a hit from this.
I thought jacquesm might be ahead of the curve on something here or that he knew some trick for multiple category ranking or something.
I'd also imagine that it increases the instantaneous value of the domain from a sale perspective as a wider range of pages can be presented in the SERPs on a domain that has many subdomains if some subdomain is relevant to a particular search alongside the main domain.
Was just a thought really, thanks to jacquesm for answering.