I believe I'm seeing new PageRank values on a couple of sites, though I don't keep precise record of this data. Is anyone else seeing this?

Yes. I saw this on Saturday I believe on one of my sites.

There was an export of the PageRank last week.

Yes. Quezi previously had no toolbar page rank, and debuted at 5. I think it was on 2nd April.

I noticed that on one of my sites about a week ago.

Yes that's i noticed it to, it was april first. In the Google Webmaster Help centrum a Google employee sayed: "I'm pretty sure we'll have another Toolbar PR update this year. However, as touched upon by the others, this is generally not something you need to worry about".