In its simplest form, an air cleaner is a big fan that pulls air through a filter that traps the dust that is floating around in the air. I think that they are an underappreciated component of dust control.
Here's my take on dust collection strategy.
1. The best thing to do is to trap the dust at the source, before it gets into the air. As has been mentioned, due to crappy collection hood designs at the tool end or other factors, this is nearly impossible to do with tools out of the box. So everyone needs a back up plan to take care of the dust that escapes.
2. The best back up plan is to vent the air (and dust) outside. Since you have a garage, opening the doors and placing a fan in another window/vent to draw fresh air in and vent the bad air out is a viable idea. But this isn't always a viable solution, especially if you live in Edmonton and it's wintertime.
3. Lacking a fresh air vent system, an air cleaner is the next best thing. Where air cleaners come up short is that the conventional wisdom is to get an air cleaner with enough CFM to exchange the air in your shop 6-10 times an hour. I went for 25-30 air exchanges per hour. You can bring down the dust concentration in the air much more quickly by increasing the number of times the air gets circulated through the air cleaner. This is cost effective and easy to do -- all you have to do is install another air cleaner. This is especially easier and cheaper than to trying to upgrade your dust collector to a cyclone system.
4. Dust masks, if yours is like
this, are pretty much useless, for two reasons. They don't provide a tight fit to your face, so dust can get around the mask, and they don't filter out the tiniest particles which cause the most damage to your lungs. Unless, of course, your dust mask is something like
this.