It depends the person. Me, no, everyone I know, no.
Your clients, I don't know.
It really depends - I mean, had it been http://online.canada or http://online.saudi-arabia, then well, I think it would scare people off - I know I certainly wouldn't go myself. However, if it's say online.lv, no I don't think it would. It wouldn't scare me off at all.
It really just depends the mentality of the person. It may scare some off, it may not. It simply depends. Unfortunately you could ask us, we could all say no it wouldn't, then you start your company up and it does scare them away - unfortunately we don't know how the brain works, yet.
Obviously, the more professional is a .com domain, however unfortunately more and more are being used - however, there are still plenty available, it just depends whether it's available in your name or not.
Unfortunately CNET has already taken the domain name http://www.online.com/ and therefore no one else can use it for their company, however you should also try and choose your company name if there is a domain left for it.
True, this can be a hassle and very hard - however BubHost said, if your company name is online.lv - then go for it, personally I'd be kind of surprised to go to online.com and find a company called online.lv - maybe try onlinelv.com or something like that, such as even online-lv.com, however online.lv would still work for your domain if that was your company name.