I'm in favour of a low barrier to dabble; we all sometimes think "I can't be bothered" and go after the next thing that wants our attention. But not requiring

I'm in favour of a low barrier to dabble; we all sometimes think "I can't be bothered" and go after the next thing that wants our attention. But not requiring registration seems to translate more easily to some sites than others. Say a registering user has the ability to claim a two-word sub-domain of foo.com, e.g. top.dog.foo.com, and to start setting up their data there, including who can view the data and sending email invites out to others. What should non-registering users be able to do? The alternatives I can think of are: Have a set of *.try.foo.com sites that they can play around with and reset them to sane defaults occasionally. Or, let them nab the site name of their choice but warn them it gets deleted unless they register within 24 hours. Either way, I'd like to avoid site names getting used up for no good reason. Any better ideas? Cheers, Ralph.