Site-wide links - is there a point?

Are run of site links counted towards PR?

[wanderingmind]

Many of the text link ad sellers seem to advertise run of site, site-wide links.

I know each page can transfer PR. However, what about if I get footer links from a 5000-page site? Isn't it too obvious and aren't any safeguards built-in by Google?

If there are, how come they are still being advertised heavily?

I have never got a run-of-site link so far - but am considering it if it's worth it. So far, I haven't come across any enlightenment :)