Google SERPs

Google SERPs have been bouncing around for a couple of days for one site.
One day I check the site and it is at #14, I check from a different
connection and it is down a page. For another keyword it's at its normal
#2 spot, but an hour later from a different Internet connection it's #4.
I search across data centers and it's ranked normally (with the
older better rankings). But sometimes when I search normally in Google it
is fluctuating between the two rankings.

The main competitor was apparently penalized recently and their PR dropped
from 5 to n/a recently. They have duplicate sites and might be doing other
shady things. (My sites are clean but the competitor has been around
longer and has many more IBLs.) Two or three weeks later they are back to
their normal high place in the SERPs and have a PR 0. They are now
bouncing from between #1 to #3.