I've been using it on Snow Leopard for well over a year with absolutely no problems. Runs fine with my two main Scottish banks and will report previous usage of my banking password if I try to use the same one, or even part of it, elsewhere. Does not seem to be a memory/CPU hog as reported by my monitoring systems. Bear in mind that for online banking YOU are responsible for your access codes. I would certainly not rely on some third party software to do it for you. I change all my codes bi-weekly and only use a wired connection.
I would never use banking access codes on a wireless, public access point or iPad/iPhone dial up connection.
I've not tried Rapport on my Lion systems yet. Have to admit I quite like Lion. All my main apps, Photoshop/LightRoom and, dare I say it, MS Office 2011 are all buzzing along nicely.
'Natural Scrolling' is a bit weird though. Turning the Magic TrackPad upside down works but it does not feel right. Removing the tick box in 'System Preferences' works better