I must chip in a word here.
I totally agree with some of the above observations. Notes and Exchange DO NOT compare and have nothing in common a part from the ability of sending/receiving mail.
Notes can serve up web pages and do site hosting in a snap. You can build practically any kind of web site with R5, and from the web you no longer have any clue to tell you you're looking at a Notes site (R4.6 sites were much more obvious and rudimentary).
Notes can build whole applications and link third party tools if necessary. Its stability has a proven track record and, if hosted with a rock-stable OS like Sun OS or AIX, you have uptimes that are simply out of reach of the good ol' NT and 2K boxes.
With Notes, you have a great amount of tools IN THE BOX. No need for additional licenses, you just have to activate the corresponding server thread or whatnot to get the functionality. You can even talk to external relational database with standard LS or NotesPump (yeah, I know it got renamed).
Also, a properly-configured Notes server is virtually untouchable by script kiddies and such trash. Our server gets hundreds of hack attempts per hour - none get through. It would take a highly skilled hacker to break a secure Notes box (note that I am not saying it is not possible - statistically, it is, but I don't how).
Finally, upgrading a Notes configuration is incomparably more simple than upgrading from Exchange 98 to Exchange 2000. With Exchange, you basically have to redesign your network, THEN install a whole new product. There is no easy way back if it doesn't work. With Notes, you can back up the server, upgrade it and put it back on-line without interrupting user availability thanks to Notes clustering. All Domino servers are backwards compatible to ensure smooth service for users and maximum data conservation.
Yet, I must also agree with another previous remark. Domino/Notes is not for newbies ! Your Notes experience will only be as good as the people you have serving it.
Although that might probably hold true for Exchange as well, but Domino has a much greater scope and therefore a good administrator needs a high level of training.
But you only train for Notes, whereas with Exchange you need to train for Exchange, for the SMTP server, and for whatever other service Exchange is connected to.
Of course, my Exchange knowledge is severely limited by the fact that I have been brainwashed by Lotus for the past seven years ;-)
PM