Should RSS, Atom, et al be aggregated by client or server software? Either way has its advantages and disadvantages.

Client:
• You don't have to be online while reading the feeds, as long as you've gone online to download them (though you'll need to go online to access things the feeds link to).
• Speed: once your feed reader has downloaded the feeds, you access them from your own hard drive rather than across a network.
• Client-side applications are likely to have better interfaces than applications that run in web browsers.
• Notification: I use Net News Wire. I leave it running in the background, and when it finds new items, it changes its icon to show how many unread items there are. I never have to look at the program unless I already know there's something new.

Server:
• Easier synchronization between locations--for example, if you subscribe to a feed while at work, you're subscribed to it when you get home too. You can also automatically tell which feeds you read at work when you get home.
• If the server does filtering, you can subscribe to enormous numbers of feeds without using your own bandwidth to download all the junk you want to filter out.
• Server-side aggregation can reduce bandwidth usage for publishers by only downloading a feed once to display it to multiple people.
• Assuming a web browser is to be used to view the newsfeeds, no client-side installation is required. This is a huge advantage for non-techies.

Note that using a client-side feed reader in conjunction with a server-side aggregator could provide the advantages of both. I seem to recall having heard of services that work this way, though I don't know that server-side software is available for purchase. It will be interesting to watch how these things evolve as newsfeed usage expands.