I do it all the time actually. For example, someone will be calling me telling me something/someone I need to follow up with. I can start immediately emailing the person and at least get started, if not finish the task. Different strokes for different folks.
Edit: I also use Google Maps while talking, or check for movie times while someone is on the phone.
So then on Verizon you could do everything but hit 'Send' on the email.
I too don't put much value on the simultaneous voice/data feature, but then again I have 2 phones, so I usually multitask by using two devices. Even without that though, I've never really felt a huge demand for the voice+data thing.
Edit: I also use Google Maps while talking, or check for movie times while someone is on the phone.