For me, the biggest changes since 0.7.? times is the arrival of Sigil plugins, there are about 50 of them, I only use a few but they're invaluable. Another major change since then is support for EPUB 3.0.
Added: Sigil has always been stable for me - the only it crash was caused by an ancient and abandoned Windows shell extension, which I've since been able to replace. And I can only recall one regression error that caused me any grief
BR