The issue with Tumblr is that importing RSS feeds are highly
unreliable. The import of my Flickr feed seems to work fine, but the
Tumblr feed doesn't work well at all. If you check on the
GetSatisfaction site, you'll see a lot of people complaining about
that Twitter feed issue.

Ideally what I'd like Tumblr to offer is to allow me to import feeds
and customize how they are imported. I would like the ability to add
the source or add a description to any item from a feed (a standard
thing that gets put in each import). It would be very cool if it
allowed me to group all the feeds from a certain day – for example,
let's say I upload 10 photos into Flickr on a certain day, I would
like them all to show up in Tumblr as one item instead of 10 items
that overwhelm my blog. If that can't be done, then give me the option
to import the first and provide a link to the rest.

Basically, I want a level of manipulation to the RSS feed if possible
and it certainly seems possible to me. Given that Tumblr has a high %
of reblogged content, it would be great if they allowed you do
customize how you pull in content – and gave you more flexibility on
the RSS side instead of just on reblog side.