Marlisse Silver Sweeney is right to say that a new GC will be likely to fire some incumbent law firms but, as I mentioned in my piece "So you’ve taken a role as a sole in-house counsel, what next?" - http://blogs.lexisnexis.co.uk/futureoflaw/2015/07/so-youve-taken-a-role-as-a-sole-in-house-counsel-what-next/ - you may encounter entrenched relationships between senior decision makers in the business and partners in an established law firm used by the organisation, in which case tact and care may need to be deployed by you in the process of changing firm.
She's also right that law firms need to be alert to the possibility of their position as adviser to that company is at risk when a fresh General Counsel walks through the door. Surprisingly they sometimes aren't that aware of this and I know of GCs that have been very surprised that client relationship partners haven't been straight on the phone to them, if not on day 1 at least during week 1 of the job. Failing to make that initial early contact cannot help that firm retain its role as trusted adviser to the business.
This surge in new GCs won’t be going away anytime soon, Rynowecer predicts. “The leap in new firm hires says few firms are using the transition as a business development tool,” he explains, warning firms to consider any GC announcement a “wake-up call.”