In the interest of full disclosure, I'll state that I'm happy with my D710 and that I had no issues with my D700, either. With one exception, every ham radio mobile I've owned has been a Kenwood. I'm a satisfied Kenwood customer. I'm also a satisfied Yaesu customer. With one exception, every ham radio handheld I've owned has been a Yaesu.
Having said that, I think that the introduction of the Yaesu FTM-350 is good for the ham radio mobile market. It has a few features, like the sexy display and provisions for a built-in GPS receiver, that may push Kenwood to improve their product. You will have to decide whether or not the features of FTM-350 are worth the slightly higher price compared to the TM-D710.
However, it does seem like the FTM-350 is not quite ready for prime time. The part that really bothers me, though, is that apparently the firmware in the FTM-350 is not user upgradeable. Even if Yaesu does come out with revised firmware for the radio, you will probably have to send it back to Yaesu for the upgrade. On the other hand, the firmware in the Kenwood TM-D710 is user upgradeable and Kenwood has put out a few firmware upgrades since the radio was released. Yaesu has already released an upgraded VX-8R handheld, but even Yaesu's U.S. office doesn't know if the older radios can be upgraded to the new spec.
Bottom line...I think Yaesu missed the boat by not making the VX-8R and FTM-350 firmware user upgradeable. It makes whatever bugs that might come to light even more of a problem because you know it will take a trip back to the manufacturer to get it fixed.