For me, it got me a job.
I had an interview for a training position at a very very well known IT company as a server trainer - I integrated the cube into my training presentation and afterward, for my feedback of the interview - it was mentioned that my presentation and subject matter were excellent, but the fact that I used a "brain toy" showed that I was able to multitask (I was talking while solving and still presenting) and it completely caught everyone's attention... They're still talking about the "Guy that solved the cube for his interview"
So is it useless? No - it's only useless if you let it be useless but I choose to make it work for me
Oh, and everything that most other people said too - awesome conversation starter!