I don't find other domains amateurish, but certain domains I'm unlikely to give information to: such as .ru and .ly and maybe in the future .ng but haven't seen evidence for that yet.

I think the main advantage of .com .net .org is the google boost but that might change in the future and if your product is right it shouldn't matter.

Personally I really don't like when the domain name is part of the name it makes it harder for me as typing a period in between a word seems unnatural: bing.com is easier for me than bi.ng.