Possibly but not necessarily the ISP. I've had the experience of seeing either a blank PR bar or, more curious, a different value displayed for the same page than other people see. It has been suggested that this is sometimes a result of querying from different data centers.
I don't pay that much attention any more but this hint was posted by a usually reliable source elsewhere -- Add the following line to your hosts file:
Code:
72.14.207.99 toolbarqueries.google.com
This forces the query to the "official" toolbar PR center.