I'm genuinely curious why you suggest the growth curve on this is exponential at this point? I saw this thread on HN when he originally posted it, and while it wasn't something I would personally be interested in I imagined it might fit a certain demographic. The question for me was always the staying power with a quick hit site like this.
Now having seen a wider window of stats on the site from quantcast, all arrows are pointing down and to the right. I agree that he's smart to try to sell it, but only because the longer he holds onto it the less opportunity there will be to capitalize on the original spike.
Also, looking at alexa it seems as though the period of hyper fast growth is already a bit past:
http://www.alexa.com/siteinfo/threewords.me
Still, it should fetch a pretty penny and to the right party it might be worth quite a lot of money.