The Acer 720's keyboard quality is crap. If you expect to type a decent bit on it, or use the keyboard for navigation...just don't. I've already destroyed cursor keycaps on mine. The feel of the KB is above average, but the durability is bottom of the barrel. The C710's keyboard isn't bad at all, though, and has most important keys. The C720's battery life, however, is excellent, in both ChromeOS and real Linux (though most distros have terrible defaults for cpufreqd, and pstates is buggy--expect to have to play with config files).
The C710 came in HDD or SSD varieties, and uses 2.5" drives, so gives more options for upgrading them (the C720 has a M.2 2242 SSD, which is now a common OEM size, but uncommon retail size). Also, it had two DIMM slots, and can take at least 8GB of RAM, and maybe even 16GB (the C720's RAM is not upgradeable). The C710 also has a VGA port, and an integrated RJ45. They're hardly Latitudes or Thinkpads, but far from crap, especially if you can get one for <=$150 (common on eBay).
Linux support is definitely better with the C720. Just properly turning it on and off, sleeping and resuming, don't necessarily work right yet with the C710, even with workarounds.
With ChromeOS, they come on from off, not standby, in just a few seconds.
Also, both the C710 and C720 benefit from generation CPU and memory improvements. If you benchmark them with long-running loops, they hang in there with run of the mill Core 2 Duos, thanks to their crippled caches (also, my C720 runs Dawarf Fortress ~50% faster than a desktop C2D E6600 (2.4Ghz), so even that's not a hard rule). But with bursty work, like browsing the web, they're crazy fast, compared to those. Sites that are slideshows on C2Ds render/animate quickly/smoothly on both the SB and Haswell Acers. The Atom, Jaguar, and Exynos ones are all insanely slow, in comparison (the particular models used are the slow/cheap ones, on top of them not being speed demons in general).
