Obviously. Google internally calculate the PR and all other parameters very frequently, but export it to tool bars, expternal tools only rarely - once in 3 months or even more. Obviously your SERPS change every day, not once in 3 months, does it? SEO experts no more track the PR update and it is no more a news either.
My site is still the same. I have been working for a while to make the jump from PR3 to PR4. Easier said than done it seems.