For the last month, I've been using the new beta Mail service from Yahoo! (NASDAQ:YHOO), which offers a host of nifty new features. The latest? Implementing RSS (Really Simple Syndication), which lets Web users subscribe to "feeds" of online content.

Why is RSS cool? With an RSS reader program, or a portal like Yahoo! or Google (NASDAQ:GOOG), you can get content delivered to you, without having to continually check back with a website. Better yet, it's 100% opt-in, with none of the spam that has made email newsletters a hassle for marketers and users alike.

"Currently all media is evolving, from TV to TiVo (NASDAQ:TIVO), to radio to podcasting, and now email to RSS," said Bill Flitter, the founder and VP of marketing at Pheedo. "The common theme amongst these channels is they are now under the control of the consumer."

One potential problem, though admittedly a small one: Subscribing to a feed is typically a chore, requiring that you copy a URL and paste it into an RSS reader. But things are changing; new services like FeedBurner make it easier to subscribe, as does the new Yahoo! Mail. What's more, since email is a daily activity for many Web surfers, it seems like an ideal environment for handling RSS.

The Yahoo! product integrates with other services, such as your contact list, calendar, and My Yahoo! You can even get alerts for new content on RSS feeds via instant messages and SMS.

Yahoo's ad-based model seems like one of the most obvious ways to make money off RSS. Moreover, RSS can be effective for e-commerce. For example, Motley Fool Stock Advisor picks eBay (NASDAQ:EBAY) or (NASDAQ:AMZN) can notify customers about new deals via RSS feeds.

Alas, Yahoo! is not the sole innovator. Expect Google (NASDAQ:GOOG) and Microsoft (NASDAQ:MSFT) to come out with their own email-based RSS feeds. Using technology from upstart Feedstar, is using RSS as a part of its portal-site strategy.

Yes, it's all good for Internet users -- but not so good for Internet-stock investors. As usual, the rapid pace of innovation hasn't given any single company much of an advantage in the continuing battle for online advertising market share.

Feed your need for further Foolishness:

TiVo is also a Motley Fool Stock Advisor pick.

Fool contributor Tom Taulli does not own shares of companies mentioned in this article.