Ditto on the ability to diff and version control the source. I've worked with Informatica where you work with GUI tools that on the backend stores your mappings and workflows in a database (that you really don't want to look at, but sometimes do anyway). There is a built in version control that sucks, and you can not easily see the changes you make or changes between versions. You can export your work as XML, and if you sort and filter it just right (which I did with Perl and XSLT), you can diff XML files. You miss the ability to grep for something, instead you have to click and click (and click...) to see the bit you want to see, and there are so many levels of places to override settings, it's sometimes a challenge to figure out why something is behaving the way it is. The one (and maybe only) thing I like about it are that you get logging with little to no effort, and (ok, two things) realtime control and monitoring of the processes (in a pretty and fairly useful GUI).