Well actually it's "Filtering new messages in 'Inbox' (68%complete) and progressing at a rate of about 1% every 5 minutes (has been running uninterrupted since my last bugzilla update several hours ago).
In the console I see:
(evolution:29189): LIBDBUSMENU-GLIB-WARNING **: Trying to remove a child that doesn't believe we're its parent.
(evolution:29189): LIBDBUSMENU-GLIB-WARNING **: Trying to remove a child that doesn't believe we're its parent.
(evolution:29189): evolution-mail-WARNING **: mail_ui_session_lookup_addressbook: Timeout was reached
(evolution:29189): evolution-mail-WARNING **: mail_ui_session_lookup_addressbook: Timeout was reached
(evolution:29189): evolution-mail-WARNING **: mail_ui_session_lookup_addressbook: Timeout was reached
(evolution:29189): evolution-mail-WARNING **: mail_ui_session_lookup_addressbook: Timeout was reached
(evolution:29189): LIBDBUSMENU-GLIB-WARNING **: Trying to remove a child that doesn't believe we're its parent.
(evolution:29189): LIBDBUSMENU-GLIB-WARNING **: Trying to remove a child that doesn't believe we're its parent.
(evolution:29189): LIBDBUSMENU-GLIB-WARNING **: Trying to remove a child that doesn't believe we're its parent.
(evolution:29189): evolution-mail-WARNING **: mail_ui_session_lookup_addressbook: Timeout was reached
(evolution:29189): evolution-mail-WARNING **: mail_ui_session_lookup_addressbook: Timeout was reached
(evolution:29189): LIBDBUSMENU-GLIB-WARNING **: Trying to remove a child that doesn't believe we're its parent.
(evolution:29189): LIBDBUSMENU-GLIB-WARNING **: Trying to remove a child that doesn't believe we're its parent.
(evolution:29189): Gtk-CRITICAL **: gtk_entry_set_text: assertion `text != NULL' failed
(evolution:29189): Gtk-CRITICAL **: gtk_entry_set_text: assertion `text != NULL' failed
(evolution:29189): Gtk-CRITICAL **: gtk_entry_set_text: assertion `text != NULL' failed
(evolution:29189): Gtk-CRITICAL **: gtk_entry_set_text: assertion `text != NULL' failed
(evolution:29189): evolution-mail-WARNING **: mail_ui_session_lookup_addressbook: Timeout was reached
(evolution:29189): evolution-mail-WARNING **: mail_ui_session_lookup_addressbook: Timeout was reached
(evolution:29189): evolution-mail-WARNING **: mail_ui_session_lookup_addressbook: Timeout was reached
(evolution:29189): evolution-mail-WARNING **: mail_ui_session_lookup_addressbook: Timeout was reached
(evolution:29189): LIBDBUSMENU-GLIB-WARNING **: Trying to remove a child that doesn't believe we're its parent.
Not sure what is wrong or how to diagnose "slow performance".