Thanks, that's interesting. There are several places on the web that say Queen's Medical Center, including Snopes.com and even on a blog at my.barackobama.com.
The Wikipedia listed Queen's Medical Center as his birthplace up until this version, where it was removed at 15:17 on September 13, 2006 by user HailFire. (For instance, see this version, the immediately previous version. In fact, the current entry for Queen's Medical Center still says that Barack Obama was born there.)
Not until just 3 days ago, on June 7th, did Kapiolani Medical Center appear in the Wikipedia article on Obama. It first appeared in this version edited at 13:49 on June 7th 2008 by user G.-M. Cupertino, and apparently is based off information at a webpage http://www.wargs.com/political/obama.html (from September 14th, 2006, until June 6th, 2008, no hospital was listed in any of the Wikipedia versions of the article on Senator Obama that I saw.) If you look at the foreign language versions of the Wikipedia article, some of them still have Queen's Medical Center as his birthplace. (e.g., Italian and Indonesian.)
I looked at some other genealogy websites, and another one also listed Queen's Medical Center:
It seems unusual to me that we cannot even determine which hospital was the birthplace of a very prominent person who was born in the United States in 1961.
Hopefully we will see the birth certificate. Obama the Manchurian Candidate waiting to install sharia law in the United States. What a great country we live in...............
Here's a genealogy tree on Obama that I've been aware of for several years. http://www.wargs.com/political/obama.html The base site that is, not Obama's particular tree. It has it as Kapiolani. I have a tendency to believe that Obama knows what hospital he was born in.
This site built by the Chicago Sun Times built Obama's family tree and gives sources. http://www.suntimes.com/images/cds/MP3/obamatree.pdf