I'm using Safari 4 beta as default browser on Vista. It seems that user login in MyInfragistics or the forum pages doesn't work at all and it shows endlessly the user login page. In the past I noticed that Safari is not working too much well with the Infragistics site. Maybe "not-so-perfect" CSS's?
I've tried Safari 3, and it totally chokes on .Net menu controls.
Maybe Safari works best on sites that run on Apple servers. ;-)