If you are adding quality content to another website only because they let you put your link in the footer is that spam. Some people think it is but I think most webmaster allow links in footers to get other webmaster to spill their brains all over their forum or blog or whatever.
I have noticed that I am much more eager to write back to someone if a link to my website will be visible next to what I wrote. Like I have to mark my territory or something. It’s like killing two birds with one stone. Plus I wrote the damn crap give me some credit.