Are there any performance, development drawbacks or advantages when designing views using Interface Builder?
From what I've seen until now, generating views with XIBs is VERY easy. But since I've not been developing on iPhone a long time, I can only direct you to this article that shows a sample XIB converted to Objective-C code.
http://arstechnica.com/apple/guides/2009/04/iphone-dev-convert-xib-files-to-objective-c.ars
Interface Builder anyday! :)
I'm sure there are no significant performance gains by directly coding the view.