I'm sure that I'll get flamed for this but you will not see a big difference in use. Maybe a bump in operating speed. I have a D-Inc and the wife has a IP4, so I've used them both. Web pages open slightly faster on the IP4 vs. the DINC.
I like the apple user interface better, but my phone can do everything that the iPhone can....we are not heavy users just phone, text and internet mostly. For what we use the phone for they are pretty equal in terms of use. The IP4 feels more solid and better built. The DINC has a ton of plastic.
With all that said, I will receive my new IP4S today and the DINC is history. I like being able to use iTunes to sync all of our data. Much easier than with an android based phone.