I currently have the 755p, which is pretty much the same thing as a centro (just larger) and I don't think that I'll switch completely to the instinct. I use more of the treo's pda stuff than the media stuff the instinct has.
I wish the palm products had GPS built in though, that would make the decision a whole lot easier.
We had a couple come in yesterday to get some instincts, but one of them ended up getting the centro instead. Another salesperson helped them, so I'm not sure the reason, but I think it had to do with how it syncs with the computer, and having a real keyboard.
I use a Centro right now, and love it. But, I can't wait until they make the instiinct available for employees. I don't really do anything on the Centro that I wont be able to do on the Instinct. But I don't use a whole lot of the PDA type of stuff. And with the Insticnt, you don't have to worry about your contacts, because they back up to our server automaticly. Also the navigation is handy, and so is the music store. So basicly, the instinct is for me. If I were you, I'd take a look at the features and benifits of the devices that you are interested in, and compare them with what you think you may use the most, go with the best match.