Less predictable. We thought we'd learn how to pick winners. What we learned instead is that it's impossible. Not just because luck is such a big factor, but because founders change.
Yes: become tougher and more ambitious, and less self-indulgent. Probably the single most important change is to overcome the fear of failure that makes one accept early, small acquistion offers. It's hard to turn down an early offer for a few million, but every successful startup has.
You said in FAW that you would have sold Viaweb for peanuts if you had the opportunity. Luckily the low offers fell through.
Why not add a new fund to YC for the purpose of partially cashing out founders, as an alternative to them selling early? This seems to be a missing component from the "what would have helped us at Viaweb" strategy.