"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).
Lotus' Comparisons