I never actually played one, but at least I can see myself doing so whereas a monthly fee is something I never even would consider. As to spending money on Facebook games, their quality is so questionable that I would not even consider most of them to actually be a game, I certainly would not spend money on those - I would not even spend time on them.
Lord of the Rings MMO and Path of Exile are two games I was thinking about giving a try though, both are F2P. So far I did not yet however.
I do, however, think that this model could have some positive side-effects for the game industry. It is a model where you try before you buy and, to some degree, the amount of money you spend is commensurate with how much you’re enjoying the game (hypothetically). I think the more recent trend of making a large and, in most cases, unrecoverable upfront investment, puts more emphasis on marketing than building a great game.
I agree, which is why I am ok with that trend, it used to be demos and reviews (I always prefer a demo as it gives me firsthand experience), but F2P fits right in with that too. Alternatively having a cheap base game and DLC to expand it, which also seems to be becoming more popular (well, DLC at least, the base game price has not changed much).
So far I consider a lot of DLC a ripoff however when comparing what you get for your money to the full game, but generally speaking I am ok with the concept. My main gripe is that for DLC to work for me, it would either have to be available early on or expand the game at its end instead of adding content in the middle, because by the time the DLC is available I have usually finished the game. For that reason AddOns / Expansions usually work better.
Recently I have been thinking about waiting for the GotY edition for games with DLC to avoid that pitfall 
I think it will also be beneficial if payment models can allow more niche titles to be supported by smaller audiences who are willing to pay a little more to support a game that is catering directly to them, as opposed to many mainstream games that seem to become “watered down” trying to appeal to everyone.
Definitely, I am more willing to spend a smaller amount on an indie game if it is in a category I like, most recent larger releases were underwhelming to me (mostly into RPG / TBS games). Take Arcania for example, it seems to be so basic as to have lost most of its flair, given the reviews, so based on that I am staying away from that, Deathspank and Torchlight I preordered however, without knowing much about either (other than that they are ARPGs and a few trailers).