Sorry to ask before installing, but does this support immediate redirection to site-start?
Right now it will just keep you no the same page but having it throw you out to some page or anther is a good idea, I'll see if I can iplement that. I'm thinking it could spit you out either to the site_start, the referrer (if internal), or just choose the page.
Having a publicly published login to the manager could be considered a security risk by some.
I can understand that to a certain extent but it's a snippet. So if you don't like it, don't use it

Plus you could easily hide it from the menu and make it non-searchable so that people would have to go directly to /login the way they go directly to /manager now. Plus this is almost an exact clone of the login processor file blocking and other security measures are still in place. I haven't incorporated captcha codes but I will if anyone wants it.
Now that I think of it, Captcha would probably be a good candidate for a plugin. Does anyone really use it? It's a great security feature and I think it should be available but does it really belong in the core?