It's my money. It's always my money. 
I shoot for my pleasure. I show photos for others to enjoy.
I like that I have a great range of things I can do with my XSi. Typically it's set in P mode, shooting in RAW and usually with the kit lens connected (17-55). I might use the pop-up flash if I'm taking a quick one of family or friends who are close by. Other times I will use the other modes to get the right effect, and can quickly attach and adjust the 430EX to my will (re: I can twist, bounce, and otherwise articulate the 430EX based on what I need, and can adjust the flash in camera or on the back of the flash if I'm not getting the right amount of light). Going fully manual happens whenever I need to do it.
For instance, we were at Walt Disney World early in November. I wanted to get a shot of the cars on the Test Track in Epcot. To get just enough blur from the cars I had to set the shutter to 1/250 sec, as I recall. Yup, just checked EXIF info in Aperture. It took me a few photos to get it right, but it came out fine in the end. If the info on the ride is correct, the cars are going around 65 miles per hour in this turn (105 km/hr). Note that there are almost no places to see the cars on the track, and there's no way to know for sure when to take the photo. You have to listen to the cars and nail when you think they'll be there. I took four photos; the third one was the winner.
Is that cheating to use shutter priority mode? I don't think so, but I don't care. Earlier in the thread, someone mentioned about computers. I could easily make the claim that if you've never rolled yer own custom operating system kernel and made silicon bend to your will, you've got no business turning that 'puter on. I'm not like that. I've rolled my own kernels and made my own computer, but I still like to surf the net on my Macs. I loved my old Pentax K1000 in the early 1980s, but my XSi is a far superior piece of equipment.
Fwiw, here's the aforementioned photo, cropped. Enjoy!
