tedster - 2:49 am on Jul 7, 2010 (gmt 0)
Last time I tested (admittedly over a year ago) no link juice flows through an iframe src= attribute. In fact, I was surprised that it didn't even seem to be used for URL discovery.
All that might well have changed by now, but in my book, the sure thing is still an actual link. Consider the situation where a page that holds an iframe also holds a few links to change the display within that iframe, by using the anchor tag's target attribute.