Reinventing the wheel

I have been reading another post war (I bet Oren really enjoys them) between Oren Eini and Chris Holmes.
It started with Oren dissing Microsoft's Patterns & Practices team, followed up with Chris's post and Oren's reply.

I find it difficult to understand Oren. Sometimes he'd rather write his own code from scratch (Rhino mocks), but he keeps preaching the use of known OSS solutions, such as Rails, NHibernate, or the Castle project.
But it's really strange to hear someone like that, always trying new tools, complaining CAB is too complex to explain, or that it contains too many features.
Is Rails or Castle the "simplest solution possible"? It seems to me that for an Asp.Net developer the simplest solution is keep coding the way he knows, and avoid learning Rails, as well as dealing with the performance issues.

Can I write my own mini-implementation of CAB? probably.
Can I write my own mini-implementation of O/R mapping? probably again.
Is it the smart thing to do? I doubt it.