Are you following me?
Ask this to make sure whoever you're talking to understands what you're saying. This is handy when you are explaining something and you want to make sure the other person is not lost.
Do you get what I mean?
Say this when you want to make sure the other person understands what you're trying to say. Here, you may be looking for agreement. This is informal, like the type of chat that might happen at the water cooler!
This is a handy phrase to use when you've said something important, or given a presentation and you want to see what your co-workers think. Do they have questions or comments? Just ask: "Questions, comments?"