Google has purchased loads of domains that are anything like google.com or common mis-spellings. The Guugle.org is owned by Google.
The other domains, it's hard to say. They just have their A records pointing to a Google.com IP. This could simply because the domain is unused, and the owner wants to send the traffic accessing the domain to somewhere useful. There could be a more sinister purpose.
Once Google accesses a domain and finds that it's actually an alias domain of another website (through duplicate content detection), the alias like domain will inherit the PR display of its parent. Pulling up a backlink query for the domain will show backlinks to the parent site. The parent site is considered to be the one which has the most inbound links.
The domain owner can then change the A record to their own content and be left with a false PR display. In this case, PR10.
The is no enhancement on the website's SERP listing because the PR displayed is actually fake. I'm sure Google will fix this problem shortly.
A legitimate example of its use would be x.com, which is an alias for paypal. Check out the backlinks. I won't post any others, but its use is widespread, and mostly legit. The other people don't get any gain out of it anyway, other than having a high toolbar PR for a few weeks (or however long it takes Google to recognize the domain is no longer an alias).
You people who think it will increase your real PR, you're wrong. Stop doing it.