I was messing around a little with figuring out some of the keyboard shortcuts in Wave. Here is what I have so far:

While editing:
Shift + Enter: Shortcut for “Done”
Control + Enter: Add comment

Control + b: Bold
Control + i: Italics
Control + u: Underline
Control + g: Poor mans CSS editor (JavaScript text input)
Control + a: Beginning of line
Control + e: End of line
Control + k: Hyperlink
Control + 1/2/3/4: Convert to h1 / h2 / h3 / h4
Control + 5: Bullets
Control + 6: Drops all formatting

While viewing:
Control + r: Reply
Enter: Same as Control + r
Control + e: Edit
Shift + Enter: Start replying at the end
Control + Space: Mark all as read

I’ll update this post if I find any more…