I have now spent a little more time with NB 10 and it's up to beta v. 22. I'm very sorry to report that it's very buggy. It even crashed once. Here's one of many, many minor annoyances. I have a NB version of the U2 that works with v. 22, but if I save it (under a new filename), it won't load. I think it's an end-of-file character difference: the saved file (saved in NB 10) has a 1A (hex) at its end, but the original doesn't. So this is probably remediable, but still.
The basic interface looks good, so I hope they can fix all the bugs.
