All very well until you look at the code provided:
<a href="http://pagerank.thetopsites.net/" title="Free PageRank Meter for www.mysite.com" target="_blank"><img src="http://pagerank.thetopsites.net/r.php?url=www.mysite.com" border="0" alt="Free PageRank Meter for www.mysite.com" /></a>
and the warning "You should not change in any way the above code(except the url of your site) or you will be disquallified from this free service".
Then you notice that they don’t use the now-standard rel="nofollow" property in the href or img src tags. Put two and two together and you realise that their Free PageRank monitor is actually donating some of your precious PageRank to them (because that is how PageRank works).
Clever? Yes. Underhanded? Certainly.