A Cre8asite forum thread asks Is there any conclusion with sitewides? Where Ammon Johns, aka Black_Knight, answers;
Site-wide links seem far more likely to be ignored or down-valued. I'm basing that on what I have seen generally, rather than on a specific empirical test.
Ammon goes on to explain that even when the links are in your navigation, he would "not counting them to count as separate links on each page.
Forum discussion at Cre8asite Forums.