very reliable
actually, the latest Notes platform due to come out is quite well done.
at my last gig, we ran Domino on the iSeries (used to be known as the AS/400) that we also used for operations. no downtime, no issues, no dedicated administrator required. it just worked, for 4 years.
most users are unwilling to learn another interface, so anything different than Outlook is regarded as inferior. since they have no idea what Notes/Domino does (groupware/collaboration, database, development platform, etc), when judging this platform, they are ignorant at best (lazy and stubborn at worst).
the company provides its employees with software to send email, and mantain calendars and address books. to moan about the different interface is just sentimental crap. if it works well, that is all the business cares about (or rather, a mature organization would work that way).
to those whiny users, i would like to say:
you're here to work, not to get a warm fuzzy.