Does domain parking could affect your Pagerank or it doesn't do anything at all? I currently have PR1 domain (with temporary content before) and then I just parked it at Sedo and was wondering if Pagerank will be affected.
I can't say AT ALL, a parking page is just one page, Google doesn't see it as a rich content but as you said backlinks (not much the quantity as the quality) can sustain the PR of the name
Earlier it did not affect PR, but in the last week I have observed that parked pages have grey on the toolbar.
You probably don't have any truly relevant links to your parked domain, which is likely the reason for the PR drop. The latest Google update seems to have hit pretty hard on sites without relevant links.
What parking site do you parked your domains? Does it mean they promote your domain? Maybe the sites linking to yours have high PRs.