Think small free web application. Users create a session, share the link, and friends join via the link. This is a quick, simple, free service, and user registration seems to be overkill, since the only data stored on the account would be the user's name, and it would seem a name/alias is just as easy to type upon each visit as a username and password would be.
The service is a collaborative tool, featuring communication where the name is used. So even though no additional data is stored, and I'm interested in implementing it without user registration / login, a user's name / alias is needed.
So my question is, is it better to prompt the user each time they enter web page for a name/alias, or provide a temporary alias "Guest 1 <, 2, 3, etc>" automatically and allow the user to customize it afterwards if they choose?