I'm being blunt because Tim made some extremely good points and was promptly criticised from various quarters without people (in my view) really critically evaluating what he said. I've lost count of the number of times this has happened to Tim whether it's over social network portability, supporting open source or even the whole web 2.0 concept.
There are network effects but it is not (nor has it ever been) sustainable at the hardware / infrastructure layer of the computing stack. Whilst I have previously discussed, in a number of posts, how preferential performance and pricing can be used to create network effects within a single cloud provider (i.e. through data transfer or intra-cloud api calls), these effects are relatively weak. For comparison consider the network effects associated with having a telephone number (strong) vs the network effects of cheaper phone calls between users on the same network (weak).
As far as I'm concerned the future for this part of the stack is one of invisibility, high volume, low margins and open source. This is not where the battle for the cloud will be fought.