If you have ads on your website/blog then it's commercial use. If you sell a product or service on or via your website/blog, it's commercial use.
If you use the feeds to build traffic or seo for your website/blog, it's commercial use.
Essentially the only allowed use for the majority of the RSS out there is for a private person to use the content from the RSS in a news reader for personal and private consumption.
Google and Yahoo don't own the content that they use and will not give you permission to use it... even if they attempted to that doesn't give them the right.
If you think you won't get caught or are too small for the media corps to worry about think again.
Remember that copyright violations do not require intent. If you used the content without license you're liable... period.... and the statutory amounts for violateor are huge and they triple if intent is proven.
Services like Yellowbrix, AP, Reuters, All Headline News exist to provide licensed content exactly for this use.
