(Anyway, this is rather off-topic. Because I am talking about memory error in regards to Metro apps' reliability. Meaning I am more concerned Metro apps can be unsafe without using the "unsafe" keyword. .Net apps are a lot safer unless you are specifically mark "unsafe").
Well that's because Metro itself isn't built in .NET, it's built in C++.
Also Windows 8 is independently pen-tested by lots of private sector and public sector organisations both before release and after release (that's where a lot of the critical security patches come from), and crashes on customer computers are reported via WinErr to Microsoft for fixing too, so I wouldn't be too worried that these crashes on the Win8 beta are going to lead to your computer being compromised.
And anyway, where did this "I didn't use unsafe therefore my program can't crash or experience memory corruption" mentality come from? It's easy to make .NET crash without using the unsafe keyword, or even worse, the "It's .NET therefore it's unexploitable" attitude (which in my experience is the opposite of the truth - you try making a dummy vulnerable C program and see if you can exploit it, and then try making a dummy vulnerable ASP+SQL program and see if you can exploit that, and tell me which is easier to do).