Thanks to Stephen Hackett at 512 Pixels, I now have fantastic footnotes on my site. I will do my best not to over use them. There is such a thing as too many footnotes. They can distract from the actual content and thus should be used sparingly. 1
I would suggest that the number of footnotes that is appropriate is directly related to how long the article is that contains footnotes. More than one in short blog post starts to become overwhelming. Long blog posts could probably sustain 2-4. You need to have something the more in the style of an academic paper to go above 4.
This footnote is a terrible example of good use of footnotes. This footnote is longer than my post which means that it is way out of proportion to be useful. In this instance I'm being ironic.