I have not added any registration walls to my site and I expirience a relatively low conversion rate when it comes to job alert signups and signups for professional profiles. Having the ability to show a pop-up with the relevant sign up form would be valuable.

Costumization would be ideal to allow job board owners choose if the popup should include a job alert signup (preferrebly costomizable in terms of adjusting job search filters) or professional profile signup (or maybe both)