aakk999, I think jonny6 may have seen something and created an answer. i.e. if you see a PR5 site jump to PR6 but your PR1 site stays at PR1 - you can make an assumption that the toolbar pagerank for higher quality sites is updated quicker than low quality sites. This is, of course, not true.
It could mean that the higher quality site was at PR 5.999999 and moved up to 6.000001 during an update whilst the "lower quality site" (I'm using his words for this example, not mine) might have had a PR 1.0053 and moved up to PR 1.99999
Due to the vast array of decimal places between numbers 1 and 10 - many sites may seem to stagnate whilst others increase. As far as I'm aware, there are no mini-toolbar-updates for "higher quality sites".