Hi, I've started a web design business and on each client's site I have a link to my site at the bottom:- This problem I'm concerned about is that all the sites I've made so far are adult sites. Is this a problem? Could having lots of links to my site from adult sites affect my site's popularity? Thanks for any advice on this!
Nope. If Google were to allow inbound links to affect a site's rankings negatively, competitors would be doing that stuff to each other all the time. Now, reciprocal links are a different issue.
Absolutely not. Incoming links cannot negatively affect your site - they are either good for you, or they are ignored (ie carry no link juice). If it were possible to negatively affect a site ranking by creating "bad" links to that site, then you'd see a whole lot of services being offered in this area. Don't worry about links to your site. Worry about the links FROM your site. Hope this helps, Colin.
You shouldn't worry about your links in footer. Google gives less value to it, watch this video from matt cutts explaining this http://www.youtube.com/watch?v=D0fgh5RIHdE
not to beat a dead horse, but adult links will not hurts your serps. If this were the case; adult webmasters would have the nuclear bomb of serps. Scary thought.