"Is Exchange a Notes killer?" is a topic which has occupied people's minds since Microsoft first announced Exchange. The following features can be noted now that Exchange has finally been released:
1) Exchange is not a groupware development platform.
2) Exchange is primarily a messaging (e-mail) infrastructure.
3) Exchange doesn't have true replication (where clients can disconnect and remain productive as they can with Notes).
4) Notes has a built-in development environment whilst Exchange requires custom applications to be built with Visual Basic (or other tools that support extended MAPI).
5) Development time is shorter in Notes because of (4).