Very nice your plugin.
Some days ago I sent to your personal e-mail, attached, the italian translation and also the default pot, because your original english doesn't contain the plural.
I saw that the date of last login that appear on widget is the actual date, so it minds that the date of last visit is update when the user make the login. That is wrong, because that date must be updated when the user logout, so it'll show at the next login.
Please, that's very important, before display on my blog your plugin, can you write the variation code for to solve my question?.
From Italy, Andrea