Google has pushed out a new release of its GData Objective-C Client Library that adds support for the Google Contacts Data API and YouTube API. What this means, in a nutshell, is that applications written in Objective-C (including those created for the iPhone) can take advantage of features like uploading video to a YouTube account or directly editing their Google account contacts.
In fact, the new GData Objective-C Client Library is completely compatible with the iPhone SDK. Per a Google blog post:
"Perhaps you want your iPhone software to send photos to a Picasa Web Albums account, or keep a journal of phone calls automatically in Blogger. Maybe your iPhone application accesses a database of information from a Google Spreadsheet or from Google Base. With the Google Data APIs Objective-C Client Library, creating software for these tasks is straightforward."
"If you are writing iPhone software, just drag the "GData Sources" group folder from the GData project file into your iPhone project, and use the GData APIs as you would when writing a Mac application. "
The Gdata Objective-C Client Library project page has more information.