As far as I can tell, Google offers two separate Open Ids to all those who have a Google account. The first is accessed with www.google.com/accounts/o8/id and the second is just your Google profile url.
1) Why are there two different Open ID?
2) If I use 1 Open ID on one site and the other Open ID on another site, are these sites associated? For example, on if I sign up to StackOverflow and SuperUser using different Open Ids, will my accounts automatically get associated?
3) Are there any advantages/disadvantages to using one or the other? For example, is there any information on how many sites provide logins for each method? Is Google considering phasing one out or combining them together?