I've been using TB of late and have my VFEmail acct set up in it. I have noticed an occasional inability to login over the past couple of weeks. Yesterday afternoon, for example. I only log in several times per day, so I can't say how often this happens. Maybe once every few days. I've never submitted a support ticket or posted at their forum, since it has never been a 'work flow' issue for me.
Today it's logging in fine on TB, btw. And I just checked the webmail login (RC) and it's working fine, too. If/When login failure happens again (before the server move), I'll mention it.