Some responses to others' comments follow. Basically, if you are good at what you do, you should be excited, or at least not worried. If you are a substandard worker, be concerned.
Ashereng (Petroleum)
"One of the reason a new owner would buy your current company is that he/she believes in it, that it will be profitable."
FACS (Mechanical)
"Most people/firms that buy a business do so because it is already successful. Most of the time you have nothing to worry about."
Another reason is that they DON'T believe it is viable in its niche, but want to get the client list before someone else does. This happens often. If this is the case, the plan is to probably phase out your existing operations, and morph their client-base into the other company. If this is the case, all employees and material holdings not carrying their share will be released. But worthwhile employees and materials will be retained. And stellar employees will probably be offered better positions.
SomptingGuy (Automotive)
"...I've lost count of the number of owners of that business - at least 4 or 5...But it's the same people sitting in the same offices doing the same work for the same clients."
The same case applies to my former employer, USFilter. While I worked there it was sold twice (in other words, I worked for three "different" bosses. Nothing changed, except some minor procedural stuff. Since I've left, it has had at least two new owners that I'm aware of. I'd bet, again, that nothing's changed, except some minor procedural stuff.
Remember, amateurs built the ark...professionals built the Titanic. -Steve