Sorry Jeremy, I was not clear in my last response. When I activated the plugin on the default theme, I was taken to WordPress.com and I logged in there successfully (as far as I could tell), and I was redirected after the login back to my dashboard on my site, where I was strangely asked to login again--but could not login with any user registered.
So again, I have a WordPress.com account and was logged into it just fine when I activated the plugin and it registered itself that I had an account on WordPress.com...but following that confirmation with the reroute back to my dashboard, I was suddenly locked out.
This sounds pretty clear to me that it is likely an issue either with my server/database or possibly my theme. But it's so wonky I can't tell. On the support forum for my theme, no other users have noted this issue with Jetpack. Perhaps I'm euchred.