At the moment, alternative, preferred strategies include:
For example, bibliographic software providers post useful answers and the occasional advert to the BIBSOFT discussion list. It is generally seen as acceptable to post an advert if you are providing some relevant free services or information from your Web site.
The first (forcing registration) may prove to be less popular as time goes on: Hotwired has recently opened up much of its site to non-registrants. It seems likely that lots of people forgot their password and either re-registered each time they visited, or pestered the site to tell them what their password was (HotWired has a special email address for password enquiries). Additionally, many people will simply pass the site by, because they cannot be bothered to register.