User profiles in Stack Exchange have typically been a very personal thing and the attitude towards them has been the most laissez-faire in the spectrum of SE policy. It is usual for user profiles to include links to external sites, as this is e.g. the place for users to link to their personal webpages or blogs.
Is there any specific content which should not be placed in that area, or which could lead to a suspension? Should I refrain from e.g. promoting Quora in that space? What about Physics Overflow? If such links are allowed, how does this match with the existence of suspensions for 'promotional content'?