Mac OX 10.2.8 and using Lotus's demo at
http://www-10.lotus.com/ldd/inoteswebaccessdemo
Firebird showed errors during loading the page (Some library missing) after logging in but would not let me send e-mail. It allowed me to fool around with preferences and most settings though. And the speed (for my Pismo/400) was not bad at all.
I think its going to take a few more tweaks to get it working - as usual us second class citizens will have to wait for Lotus/IBM to bestow their kindness on us Mac users!