Sebo_fan, yes, it's true that bagless vacuums can pull out lots of fluff from carpets. Another issue with bagless is that dust tends to collect on the OUTSIDE of the vacuum body.
Before Dyson came out, market research showed that people wouldn't be happy with a clear bin for the dust. James Dyson and his team decided to make a clear bin anyway. Now clear bins are everywhere, although they're not all made of the same plastics. My Dyson DC07's bin is made out of polycarbonate, which is a tough plastic that bounces back. My Hoover Windtunnel's dirt cup is made out of plastic that shatters.
Yes, many bagless machines expel dust back into the air, which is the reason why they smell. Now, some higher-end machines, like Dyson, Shark and Miele, utilize completely sealed systems that won't kick dust back into the air.
I don't think anybody read my first post, so here's how the test went:
1. I vacuumed the carpets with the Hoover Windtunnel.
2. I immediately went over the same areas with the Eureka AirSpeed.
3. The mountain of dust on the Eureka paper was what was left in the carpet AFTER using the Hoover.