Just a quick note for those who have not seen this yet, but eBay are no longer charging for "API Calls, Program Membership and Application Certification ...", from the press release.
In addition to this they have launched the eBay Developer Challenge 2006, an interesting looking competition with plenty of stuff to be won.
The eBay Developer Challenge 2006" ("Contest") begins at 12:00 AM PT November 14, 2005 and ends at 11:59 PM PT January 31, 2006. Contest is open to confirmed registered members of the eBay Developers Program, who are legal residents of the United States and the District of Columbia, 18 years of age and older. Void in Puerto Rico and where prohibited by law. For complete details see Official Rules.