For those who haven't checked the web site yet, the conference is June 1-4, 2008 in Long Beach, California. The registration fee is $895 USD, $995 after May 5. The site has links with details and costs for hotels near the conference center.
I was checking out the conference details and discovered that admission is free for presenters so you can save $895. That might make it easier to get permission to go from the boss. You must submit an abstract by Feb 18, 2008 and it must be accepted. For more details see this web page.
http://www.ptcuser.org/2008/cocreate_cfp.html