Having owned a Dyson DC25 for a few years, it had begun to struggle and the suction, even after new filters, was deteriorating. I suspect the building/plaster dust didn't help! Plus the dc25 was shockingly useless on hard floors.
As I only have a 2 bed house, I chose the dc50 as the appropriate replacement. I was particularly interested in it for the auto adjust base plate for hard floors and carpets. The size and weight weren't important to me.
I wasn't expecting mass power when I bought it so I was very pleasantly surprised when I turned it on and did the carpet. It's made it look revitalized and very clean indeed. Everything about it bar the wand is better than the dc25. Quieter, sucks up more dust, less pipes so you can get along skirting boards better. Plus it's really good on hard floors too. I'd read somewhere that it wasn't that great on hard floors because you had to turn the brush bar off, so I was hesitant at first to consider this machine. However, having read the manual and dyson website, it is total nonesense that you can't have the brush bar on. Dyson instructions (or at least the picture) shows it should only be turned off on rugs, which I suspect means shagpile or something that might jam the bar. Plus other reviewers state that the quality of the plastics seems flimsy. Whilst I agree it doesn't feel as robust as some of the earlier models, lighter and thinner materials doesn't always mean cheaper. Who cares anyway when you have the 5 year warranty.
All in all, a brilliant machine, easy to set up, easy to use, great results and exceeded expectations.