This Techcrunch post brings up an interesting point by comparing Friendfeed to Meebo. Meebo's first step was to aggregate the IM networks on its site, offering convenience to consumers. Now it is trying to capture a lot of the value (away from the original IM networks) by moving users to its own IM network and by adding other complementary services that will keep them there. In theory they will then monetize them and justify their valuation. But that's another story.
Friendfeed is pursuing a similar strategy. First they are aggregating activities across a bunch of web services. At the same time, they are adding new functionality: in this case an underlying social network, conversations, search and I assume filtering/personalization will come soon. These will keep people coming back to Friendfeed (as opposed, in many cases, to the services themselves). Their upcoming API will allow people to do more interesting things with this information, but more relevant to this post, may also allow people to post things/interact with all those web services that are being aggregated (without actually going to their sites). In this way they will abstract users away from all those services and capture a pretty big chunk of their value.
Some of the underlying services won't be happy about this, but they can't do much about it (other than shutting down access and really ticking people off). This aggregation/abstraction dynamic is a fascinating by-product of the nature of web services today.