GTK+ failing to build, Xcode 3.0 is the culprit
root# port -v install gtk2
–––> Extracting tiff
On Mac OS X 10.5, tiff 3.8.2 requires Xcode 3.1 or later but you have Xcode 3.0.
Error: Target org.macports.extract returned: incompatible Xcode version
Warning: the following items did not execute (for tiff): org.macports.activate org.macports.extract org.macports.patch org.macports.configure org.macports.build org.macports.destroot org.macports.install
Error: Status 1 encountered during processing.
If you're being given this error message too, as the error suggests you need to grab yourself a newer version of Xcode. Since I only just reinstalled Mac OS X Leopard on my MacBook Pro I installed the Xcode that came on the 10.5.6 DVD which as the error above shows is only Xcode 3.0.
What's curious is the Apple Software Update has never told me about a newer Xcode. Is it because you need to login as a ADC member first perhaps?
Anyway, lesson learned: make sure you have the latest Xcode before attempting to compile software or built ports on your Mac! It's not that it's darn obvious you should, but that we need reminding sometimes :).