When Cycle 8 came out there were dozens of people that crashed their installs by not updating prerequisites before updating the Xamarin for Visual Studio extension and that resulted in LOTS of posts.
Before you update to the new 4.3.xxx (Cycle 9) be sure to follow @JamesMontemagno wonderful guide. It will save yourself a world of heartache.
And be sure your VS install qualifies. It is not for people stuck on VS2012.