I don't see why people make a big deal out of this. How often do you really need to talk AND use data at the same time? I've never, ever, ever, ever, ever had to or even had the inclination that I wished I could. I think it's one of those features that sounds cool, but in reality no one really uses.
Add in using it a Wifi hotspot, and getting your VPN connection/download/SSH session/whatever interrupted every time your phone rings would be REALLY annoying.
It'd be worse if you're using it as a hotspot and you're sharing the hotspot with other people.
It's not essential, but it's not useless either.
I also hate having some sync operation get stopped because I get a call.
It's more annoying than you think but not a total deal breaker.
*Not what you think... usually pictures of the cat or what I'm cooking.
Also talking on the phone and needing to look up a reference happens surprisingly often. It's really nice to have data available while talking.