I was one of those who flipped from using Netscape to IE.
I was using Netscape since 2.0 days. Comparing Netscape 3.0 to IE 3.0, Netscape won handsdown. It had far more features than IE 3.0 and was fast, responsive and easy to use.
Then came Netscape 4.0 and IE 4.0. This was were Netscape failed horribly.
Netscape 4.0 Communicator was slow and buggy and crashed often. When Netscape 4.0 Navigator crashed, it brought down the entire suite (Email client, Web Composer) along with it.
IE 4.0 on the other hand was really slick, stable and cool. It loaded up faster and rendered the pages faster (bear in mind those were the days of dialup).
It didn't matter that IE 4.0 was bundled into the OS. I was using Win 95 and I downloaded and installed IE 4.0 because I loved it.
To me, it wasn't the bundling of IE 4.0 into the OS that killed Netscape, it was just that Netscape 4.0 sucked compared to IE 4.0
After IE 4.0, I discovered Opera and have been using it since.