Recently our old vacuum decided to give up the ghost on us. It didn't go out with a whimper - it actually scared the hell out of my daughter who was using it at the time.
I thought she had tried to vacuum up a Lego or some other hard object, which then got stuck in the beater bar, jamming the motor. I grabbed a screwdriver and took it apart to see what happened, and found that half of the impeller blades were broken, which actually broke the whole motor assembly case. Not an easy/cheap fix, so we tossed it out and got a new vac.
The two main choices for us were traditional bag vacuums and the newer style bagless vac. We've always had bag vacs in the past, and it always seems that we're running out to buy bags. We gave the bagless style a shot this time around. A Hoover 12amp, to be specific.
In this case, the dirt is sucked in to the main chamber on the left. A fine screen separates that open chamber from the filter on the right. Small dust gets through the screen and trapped on the filter. Anything which gets past this filter gets picked up by one of two more filters. Compare that to just a single bag designed to trap everything.
On the downside, the available space to hold the picked up dirt is small compared to a bag, but considering you can just empty the collection bin be back in business in a minute, it's a small price to pay. Typically I end up having to empty the bin after a full vacuuming of the house. If I don't do this, it blocks the screen and filter too much which reduces suction.
Here's the empty vac ready for action.
After just a few minutes and two rooms, I've got a good collection of dust going. This brings up the real down-side of a bagless vac - you end up seeing just how much crap you've got in your carpets. With two kids, two adults, a dog and a cat in the house, this can be pretty nasty looking at times. Dumping the container can get a little messy, since everything isn't contained in a simple-to-dispose-of bag.
One thing I've noticed is that after vacuuming my allergies usually do not cause me too many problems. With our old vac, this wasn't the case. I'd get a bagless again in a second. The hastle of dumping the container after each use is minimal compared to how creating a dust-storm every time we clean.