I was reading about PostSharp, And I see that it uses compile-time weaving.
I know that PostSharp is a pretty mature, but is its weaving system safe enough for commercial use ?
Has anyone ever encountered problems, or knows of problems that can be introduced by compile-time IL weaving ?
I'm going to point you to their customers page http://www.sharpcrafters.com/customers because that says enough to answer your question.
YOU are ultimately responsible for making sure the aspects YOU build are correctly implemented. If you're relying on a "black box" process then you shouldn't be releasing software. Postsharp is a mature product and I have personally released several commercial products to clients with Postsharp enabled features.
Get yourself a copy of ILSpy and make sure you understand how PostSharp works because you can't blame Postsharp weaving if you write bad aspects. Learn Postsharp here http://programmersunlimited.wordpress.com/postsharp-principals/