The choise of format doesn't depends just of size or resolution. There are many other factor to take into consideration.
Correct!
I'm saying this, because I also had the same question myself, and I ended up by staying in the 35mm format. First, because of money - dont have money to spend in new cameras, lenses, and a MF scanner. Second, I also use a digital SLR, and this way, I can easily use all my lenses in my Nikon's digital and film cameras, wich is much more pratical. Besides, I can choose among of many other types of lenses, while MF the choice is much more reduced (no VR/IS, no tils and shift, no long zooms or teles, etc.). And then, there is also the subject issue.
It is true, 35mm is far more convenient than any other format.
I think most of the posters here shoot nature or portraits? Or still-live subjects? I would like to see a MF photo of a sports event, wildlife, streetphoto, photojournalism. What is the best fps a MF camera does (film, not digital)? 2, 3 fps?
Yes, you are not going to get much more than 2fps at best (doesn't matter film or digital, they are all equally slow and the AF speed is not much better either). On the other hand, street photography? Come on, medium format has been used for ever for street photography unless your idea of street photography is picking off strangers with a 200mm lens at 5fps.
As for wildlife it depends what kind of wildlife. Yes, if you need to shoot birds far away or lions half-way throught lunch, a Canon 1V with a 600/4 is probably a better idea. A 1Ds with a 600/4 is an even better one. But wildlife is not impossible to do wit MF. Salgado shot the Galapagos with a Pentax 67 and TriX (if I remember correctly) and Nick Brandt creates his very distinct wildlife images with a Pentax67 as well.
And how much do we have to pay for a good MF scanner (dedicated, not a flatbed), if they still producing them?
Why a dedicated one? I use a V700. If I want better quality I send it to a lab and pay the premium for the one or two frames I need vs spending lots of money on a dedicated MF scanner and then spending hours trying to get scanning right with it. You don't have to scan everything yourself, it is more economical and time saving to sometimes outsource things.
I truly respect the obvious qualityes of MF, but sometimes the optimal is ennemy of the Good (sorry, dont know if this proverb exists in English). And for my needs, I realy prefer a much more "elastic" and cheaper system like the 35mm can offer.
I use both 35mm and MF. I use 6x6 and also tried 645. The only reason I decided 645 is not for me was that it was more close to square than rectangular. And if I am not to use square, I like to have something that is obviously rectangular, like 35mm. And the issue I now have is that if I want to do a more rectangular 120 format, then I have to move up from 645 and 6x6 to the other formats. Where the weight and size issue is indeed an issue.
But apart from that, 645 has the same tonality and resolution and look that pretty much any other 120 format has, which is far nicer and softer-yet-sharper-and-contrastier than 35mm. If I could have a 645-sized camera with a more rectangular format I'd pick it straight away, vs using a 35mm.
But each system has its use.
One last thing: cost. Is 35mm really cheaper? Yes it can be if you buy an Olympus OM1 but then the overal capabilities (AF/fps) are not much better than a 645 camera. But what if you want a more modern 35mm camera with all the bells and whistles? Probably a EOS 3 or F100? Either of which is £100-150 in the UK. How much for a 28/50/85 kit? In the UK used market, a 28/50/85 kit will cost you a minimum £450-500, so you are looking at £600 total for the camera and lenses. If you opt for a f/2.8 zoom, then you could bring this down to £400 (say a Tamron 28-75 and a EOS 3). I know the prices, I bought such equipment in the last year.
If you do not want the fps you can get the cheapest of the cheap 35mm bodies (an EOS 300V or F55?) for £10. So your 35mm kit costs are £400-600 for a basic kit.
Compare that to a 50/80/150 645 kit. Such a Bronica ETRS kit with prism and winder will cost you £300-350. A similar Mamiya 645 can be had for maybe £100 more than that.
Well, they are obviously not the same capability, fps vs hand crank, small film vs big film look etc. But you know the differences, the point is that it is not actually more expensive and the initial equipment cost can be less than 35mm. And God forbid if you want a Canon 1V or Nikon F5. That's almost Hasselblad money.
Anyway, I'm rambling on. Is 645 pointless? No. It has a very valid use and I would use it instead of 35mm if I liked the format ratio. But I don't. So I continue with 35mm and 6x6. Either format has a use. 35mm for convenience and certain types of photography. 120 film for other types or a different look.
Not sure why people (not you) go on about things in a "I have no use for this therefore it is useless and crap" way...