Integrating with VS is definitely a non-trivial task. But I work at Microsoft and have access to all of the VS source code, so that's a big help. And when that fails I can usually track down someone who owns that feature. But usually it's only an issue when going off an implementing some brand new integration point for the 1st time, most of the time is spent working on our own bits.

As Dino said it's not trivial, but one of the reasons we fought hard for open sourcing it was to make PTVS a Real World sample in case someone else wants to do a plug-in for their language. We know of at least two major companies that are checking it out for that purpose.