Also wondering about this. Interviewing at Pivotal this week. Should I be reconsidering?
The most possible disruptive outcome is that Pivotal spins out entirely, but I don't see that happening for a while, or even being influenced one way or the other by the Dell/EMC deal.
I wouldn't worry about it assuming you've got a timeline for the next 12-24 months.
As an aside, Pivotal also heads up Cloud Foundry, which is an open source PaaS that runs on top of every IaaS. We have been good at selling it to large companies (I work at Pivotal). Everyone in this thread is wondering how EMC breaks into cloud computing, but no is mentioning Cloud Foundry. That's currently the tip of the spear.