Datamation takes a good look at the RSS Reader / Aggregator market and also shares some interesting FeedBurner stats, based on the 1,000 most popular feeds they're serving.

Here's the complete list of the top 20 Readers:

My Yahoo* -- 59.02%;
Bloglines* -- 10.42%;
Firefox Live Bookmarks -- 4.20%;
NetNewsWire -- 3.74%;
iTunes -- 3.37%;
iPodder -- 2.38%;
NewsGator Online* -- 1.82%;
Pluck -- 1.59%;
FeedDemon -- 1.56%;
Reader not identified -- 1.02%;
Apple CFNetwork Generic Client -- 0.96%;
SharpReader -- 0.86%;
Thunderbird -- 0.82%;
Safari RSS -- OS X Tiger -- 0.61%;
iPodderX -- 0.54%;
LiveJournal -- 0.52%;
NewsGator Outlook Edition -- 0.51%;
RSS Bandit -- 0.50%;
RssReader -- 0.34%, and
Opera RSS Reader -- 0.33%
(* online RSS readers)

But, as Brian Livingston, the author of the article states, these results do include some top circulation feeds, which for example come as default feeds in a new MyYahoo! page.

Here's the top 20 list with the 10 most popular feeds removed:

Bloglines* -- 19.49%;
NetNewsWire -- 10.07%;
iTunes -- 9.53%;
Firefox Live Bookmarks -- 7.25%;
iPodder -- 7.17%;
My Yahoo* -- 6.68%;
FeedDemon -- 4.23%;
NewsGator Online* -- 3.83%;
Reader not identified -- 3.07%;
Pluck -- 2.07%;
SharpReader -- 1.91%;
iPodderX -- 1.77%;
Thunderbird -- 1.75%;
Safari RSS -- OS X Tiger -- 1.75%;
LiveJournal -- 1.44%;
NewsGator Outlook Edition -- 1.27%;
Apple CFNetwork Generic Client -- 1.21%;
RSS Bandit -- 0.99%;
Opera RSS Reader -- 0.90%, and
Sage -- 0.82%
(* online RSS readers)

So what does all this mean for marketers?

a] The RSS Reader market is still highly fragmented, which is leaving the way open for branded RSS Readers, using which strong brands can further expand their reach and communicational touch points with their consumers.

b] Excluding iTunes, which is a podcatcher, the pack is mostly lead by online RSS Readers, which in a way could mean bad news for marketers on the long-run.

These services aren't serving targeted ads next to the feeds yet, but I wouldn't bet they won't start doing that sometime in the future.

The result? If this happens, marketers will start seeing their competitors right next to their own marketing communications, actually opening the door for them to take over their clients.

Jason Calacanis believes this will never happen due to possibility of infringement ...

"In this case, someone is doing an advertising supported RSS reader which is a huge infringement and something Bloglines, My Yahoo, and Newsgator don't?and never?would do without permission from the publisher of the feed in advance. If you're full RSS feed can be viewed at www.webloghub.com and they put advertising against it I highly recommend you send a them a note." [taken from a discussion on how to handle people that display third-party full-text RSS feed content on their sites and serve ads next to them]

I wish I could be as confident as Jason about this issue ...