if you mean buying advertising, it is ok. social networking sites were not meant for advertising by posting links. dropping a few links here and there, will not cause any harm. if you overdo it, it will be considered spam and somebody may report it to google.
No, not buying sachin, I'll just scrap members in a community that's related to my blog... is that okay.. !
Why dont you advertise your website on Communities. This way it wont be spam and you'll get visitors to your website also i am telling about the Orkut Communities. You can place links on the main description of the communities For more details you can pm me
Yes it is allright I guess to advertise your site in social networks. You can get more traffic to your site that way.
You can do it without any hassle, as long as you didn't click on your ads in the article you submit to social networkers...