I worked for a small company acquired by IBM in 2011. We had a good 5-6 year run where our product sales went up (largely because so many IBM people were selling it) and we were largely left alone. Once things slowed down a bit the IBM rot set in quick though. These days I think all that's left is a skeleton crew maintaining the obligatory long term contracts around the main product, every other part of the original company has been picked clean.

You can measure it by how many management steps you, as an employee of the recently acquired company are from the CEO in the hierarchy. As time goes on, this number tends to increase. It used to be easy to see this in Lotus Sametime or something that had some form of employee directory.