Here is an example case where I think a disclaimer should be necessary:
How to watermark a folder of photographs?How to watermark a folder of photographs?
The interesting thing about this particular answer is that the account name of the person who answered is the name of the company that makes the software being promoted. I am not sure if we are willing, as a community, to accept such an account name AS a disclaimer...or whether we want it to be explicit. I'd like to know what peoples thoughts are on this specific case, and the general type of case involving an affiliated individual promoting specific products.
My own opinion is I don't care for it much. I don't think our forum should be used as a place to advertise software, and if we don't discourage such answers, it'll become a more and more common practice.