Yes, I'd expect tags to be straight underneath the entry box too, just like the title is straight above it - I consider them that closely related to the entry.

[Trivial: When the list of tag suggestions is longer than the screenspace below the tags entry box, part of the list ends up displayed below the fold. It'd be good if it could automatically adjust to show all (or as much as possible) on the available screenspace so you can see it without scrolling.]

Could Preview go next to Publish? (And then might as well include Spellcheck there too.) Unless you've got a particular reason for giving Publish a whole line to itself.

Would be good to allow custom recurrences. Every fortnight would be a popular one, surely; and then there's a difference between "the first of each month" and "the first Monday of each month". (Granted I'm unlikely to use recurrence at all myself, but these are both things that come up in my personal calendar.)

But in general, this is very very cool, and I'm looking forward to it going live!