I try to navigate via keyboard as much as possible, so this may be less an issue for most. My normal workflow for composing an email in a web-based my clients is:
Click the compose button
click inside of the "recipients" box, type the email address for the recipient, hit tab, which takes you to the subject field
type the subject of the email, hit tab, which takes you to the main body of the email
type the body of the email, hit tab, which takes you to the submit button
hit enter to send the email.
In Roundcube hitting tab out of the body of the email takes you to Charset selection. another tab takes you to Editor type, then up to the buttons at the top of the page (e-mail, address book, etc), 9 or 10 clicks later you eventually find Send.
Ideally, I think, it would be nice if the Send button were next on the tab list after the body of the email. Since you've already got your hands on the keyboard it's nice not to have to reach over for the mouse in order to send the message. I know there are probably only a very small percentage of people extensively use keyboard navigation, for those that do I think this would be a plus.
Thanks,
d
