I've only ever had this come up one time... I was talking to a friend and he asked me to look up something on the Internet... Couldn't do it without hanging up the call and calling him back.
I can certainly see how being able to browse the web and talk at the same time would be a nice thing, but since it's the fault of Verizon's network (and not just the Droid, specifically) it's not something that's going to cause me to drop my Droid for another phone. Verizon's other qualities (great 3G coverage, very few dropped calls) outweigh this one disadvantage, in my opinion.
Mableton, Georgia, USA
And with Verizon adding LTE sometime in the near future, this will not be a problem ever again. I'll be sticking with Verizon because their coverage is amazing, and LTE is like a big happy marriage between CDMA and GSM. Of note, CDMA is just a communication method, a radio type. CDMA2000 is what Verizon uses, and is more advanced than GSM. The GSM providers with 3G, unless you count EDGE, are not even using "GSM" anymore. UTMS is a more advanced and better developed version of CDMA communication standards.
Of great note, LTE continues the CDMA advancement of UTMS, and even more amazing is it's completely backwards with all CDMA standards, as well as GSM. For CDMA, that includes CDMA2000 (1x, EVDO), and W-CDMA (UTMS).
It isn't the case that LTE simply incorporates all of this, but rather, will seamlessly handle and pass services from LTE to those services whenever necessary.
I don't feel like looking it up again at the moment, so I cannot remember specifically whether LTE technology itself will handle connections of the backward-compatible services, or if it will simply pass it to a compatible tower.
What I look forward to is having a Verizon 4G(LTE)-equipped phone, and whenever I have 4G service I'd have the capability to reach some insane data speeds. But I wouldn't have to worry about coverage, because if I don't have 4G service, I'd have plenty of 3G and 2G coverage elsewhere so while download/browsing speeds will be slow, phone coverage will never be an issue. Verizon's network is one I've never had a problem with coverage-wise, and dropped calls are so rare they basically don't happen on my end.