This is one of those services that are a little confusing and usually end with the phrase, "I guess that is what you would call that".  Planetaki is a really pretty RSS reader fetcher.  You take your content from this place, from that place and from the other then combine it into one big lovable planet.  You can choose to share that planet with others or keep it private. 

To get a taste of what they have to offer, check out the demo for yourself. 

Some of the "pros" for this service is that it makes it easy to combine sources into one place, it can be used for corporate use, it works on the iPhone, and it looks like they are really working hard at making the service better for everybody.