Yep, 'tis true. :)
I can hear it nearly every time within half an inch if stitching.

This was going to be my suggestion as well. My brother also has a warning notice that pops up on the screen when my bobbin is low. Of course it usually pops up when my bobbin is still half full, so I have to constantly be checking so the same doesn't happen to me. When the fuzz and lint really starts building up inside my bobbin case area, my bobbin indicator stops working all together and I know it's time to get my machine serviced.

I now know to brush out my bobbin case area with every bobbin change so that it doesn't build up so badly.

Take it in - I had the same problem one time and I am so used to that signal that I just can't sew without it. I have a preventive maintenance policy so I take my machine in quarterly just for them to give it a really good cleaning but I can take it in whenever I have any problem, no matter how minor.

Use a bobbin for the top thread, so they will run out together and you will notice it! (A hint from my quilt guild)

It also won't work if the bobbin case door is open. Ask me how I know.

I find a can of pressured air really works well to clean out all those un-reachable areas. Get it at the office supply store.

When I use a very fine thread, my bobbin low warning seems not to work. Try a bobbin with different thread.

Since I only sew on a vintage machine, there is no warning and I don't really need one. I always notice immediately when the bobbin thread has run out.

Also, I read that using pressurized air and even blowing is not recommended as you can blow loose lint further into you machine causing more problems.

I have a Babylock and if I wind the bobbins myself the bobbin warning works pretty good, however I use a lot of prewound bobbins and they apparently have a lot more thread on them so it warns, and warns, and warns for the last fourth of the bobbin. It is not all it's cracked up to be!

My dealer told me the same thing. He said it's fine to use on the outside of the machine to blast of general dust and thread lint, but for the inside it's a no-no. I use a skinny paintbrush with splayed-out bristles and a chenille stem to snag dust from deep inside the machine and it's amazing how much stuff I can find within reach to pull out of there...who knows how much stuff is out of reach!!