a16z - also Chris Dixon - led our round at Keybase. We only have great things to say about both the firm and Chris. Chris sits on our board and has been a class act the whole time.
Also: during our fundraising, we faced a number of the "Monday pitch meetings" -- this is where you've gone through the early crap talking with VC's and are invited in to pitch to the partners. It's typically the last step before an offer. a16z's partner meeting was, by far, the most tech-savvy and aware group. It seems obvious that VC's would understand the technology they're investing in, but honestly, that's often not the case. We faced a lot of brand-name VC firms that couldn't understand what we were working on. We'd get a sense of that and quickly adjust our pitch to focus on what they could understand.
For those asking "Why give them so much credit when they're just doing their job?" -- there are special occasions when a startup's interests and its investors' interests are not aligned. The first big opportunity for a VC to mess with you is the period between a letter of intent and closing the round, when all the smaller details come up and are negotiated. a16z was excellent in the process and we closed quickly without issue.
A later possibility of disagreement is what ar7hur describes here, and here's why it happens: VC's have zero risk aversion and aim to maximize expected value in dollars, which is what you'd want as an investor in the VC. But especially if you're a first-time founder, your dollar-to-utility curve is anything bit linear. Most humans wouldn't trade $5 million for a 1-in-10 chance at $100 million. This discrepancy is the source of a lot of possible problems. How VC's behave during both subsequent rounds and possible exits is perhaps the most important measure of them from a founder's perspective.
tl;dr very happy with a16z and Chris Dixon.