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I thought everyone knew that directory and toolbar PR are updated at different times, so don't necessarily show the same thing. We took a nose-dive in directory PR in the last directory update, but toolbar PR remained as before.
If your PR7 site shows as PR0 in the directory, I'd be worried about a drop in the next toolbar update. How are your serps? A PR0/penalized site is unlikely to get good serps, so if your serps are stable, chances are the directory PR is inaccurate -- at least that's what I'm hoping.
It appears there are now more sites listed in the directory, even though DMOZ still shows the previous figures -- actually a 3.5 percent higher count in Google over DMOZ. This is weird. Anyhow, I'm not seeing evidence of a directory PR update, so it may just be a re-shuffle to include those additional listings. Not sure where this data is coming from though!?!
Something similar happened with my site after Allegra. I had a mess with the 302 hijack/canonical problem (fixed, but Google still doesn't realize) and my website listing dropped towards the bottom of the Google directory and showed no PR.
My index page still showed a PR 5 until the last PR update, many months later, now it's zero, nada, zilch. Interesting enough, some other pages still have PR.
Similar to what LegalAlien stated, I'd be worried if your stable serps took a dive. Otherwise, it maybe it's a glitch and will sort itself out. I'm keeping my fingers crossed for you!