The implementation varied across the three companies that I worked with, but each time we used either IBM or one of their partners to help with the implementation. There was really little room for error that way and it made sure everything was done right in the end.  

I have deployed it twice by myself, with no help from a vendor.

We used an integrator for the integrator. 

We used an IBM partner, who were still learning the system.

In-house, but with help from a hired contractor who was recommended by the vendor.

IBM supported aspects of the implementation.