You can continue to depend on it as long as you like. The companies that should be scared about this trend are the large commercial vendors who develop very closed proprietary products. Bill Gates should stay awake at night worrying about this trend. It's already happening. Web broadcasting company Wave-Top recently replaced all of their Windows NT file servers with Linux, and found their performance went up and maintenance costs went down.
Open standards win.
What this means for vendors is that they should be vying to be more open than their competitors. Users of closed products should ask themselves why they use that product. Customers will buy the more open solution. Over the long run it pays off for them. Open standards win.