I love the groovy scripts. I feel as though they give me the freedom to do nearly anything I need to. It makes dealing with any webservice very easy and flexible!
I love load tests. They make my life very easy
I like being able to quickly make a sample request for a webservice, and update it on the following releases. If I just need to make simple requests, I can do it without needing to build a test suite.
I've seriously become a major advocate for soapUI. My current job is my first exposure to an SOA based system, and soap has become an invaluable test artifact.