You will get conflicting opinions here to this question. You have the die hard .com domainers who refuse to believe any other TLD could be worth anything and then you have the domains who see the marketability and brand ability of a domain.
You also get some domainers who end up buying randon unrelated single word domain in TLD's that are not at all relevant. For example lets say: shoes.poker - registering domains like that are probably not a good idea.
I do believe the alternative TLD's have great potential but you need to ensure that you register stuff that is relevant to the actual TLD.