Krzys just blogged an update that I made a bit ago to the DesignGuidelines document. It's a bit of prescriptive guidance on when to use Factory-based object creation over traditional constructors, mostly influenced by what we've done historically in the Framework. This was actually my first update to “the DG” (as it's commonly referred to), and I've made a few others since then.

The most recent update I made taught me quite a bit during the writing process... I worked with RicoM, Don Syme, and Andrew Kennedy on it (I wouldn't have gotten the facts straight otherwise!), but a whole slew of other folks throughout WinFX also had a shared interest in seeing this topic documented. It's a fairly complicated and heated subject, but the bottom line is that under certain well-defined circumstances two NGen'd images could be unable to share generics instantiation code. In such a situation, the JIT will end up being called in. This ends up being pretty bad, especially when people often go to great lengths to avoid calling in the JIT altogether... surprise!

I'll look into posting the actual DG update over the next couple days... the original email thread on which we hashed out the logic might also interesting to some folks. Maybe I can post that too, in keeping with that whole transparency thingamajiggie.

I'm currently overhauling our guidance on finalization and disposability. The internal feedback keeps pouring in on these topics, and at this point I'm in a hurry just to get something out there to stop the bleeding! ;)