Exciting news if you're looking to migrate from Lotus Domino to Exchange 2007: the development group has recently released the first wave of the new "Transporter Suite" for Domino (be sure to check out the release notes).
Exchange 2007 no longer needs a "Notes Connector" per se, since it uses SMTP to transfer mail to/from Domino, although there are some extra services (eg address book synchronisation, free/busy interchange) which are provided as part of the transporter suite.
Erik Ashby, Program Manager from the Exchange team, has been working on migration tools for years (he was behind the Exchange 5.5 Move Server Wizard, aka Pilgrim, which could lift a whole server between one site and another, and has been involved in cross-site mailbox moves, Notes & Groupwise migrations etc, ever since). There's a nice video over on Channel9 of Erik talking about & demoing the new Transporter Suite.
I posted a while back about the release of the Transporter Suite for interoperability with (and maybe