I've seen some 4 letter .net names available. Are they or will they eventually be worth more then registration fee? Thanks.
Google doesn't mind them... as long as you have good content... ;-) If you are building a site for primarily search traffic, the domain name doesn't really matter as long as it is a standard TLD (.com, .net, .org). If you are building a site for branding and off-search... .com is the way to go.
I don't think he was asking about content. I believe he was asking if the domain names by themselves would ever be worth anything. The answer is no.
If you have good content and a way to monetize them, then go for it; if for holding purposes, unless they are a standard English word (which I doubt), not worth it.
I saw a bunch of LLLL.com's for sale the other day for $10 each so you can base the value off that. You would probably have to hold them for 15 years or longer for them to have much value.