I don't think this is good enough. What if I choose "download last 1 attachments", and then after a weekend in which I haven't used my computer two new attachments appear in the feed? Naturally I'd like both to be downloaded, yet I wouldn't like more than 1 to be downloaded when I add th feed. Thanks for listening.

Hmm. If the problem is mainly for adding new feeds, how about adding an option to the feed wizard so that when adding a new feed you can specify whether existing attachments should be downloaded.

First off, it's clear there will be times when an attachment wasn't downloaded for some reason (download error, insufficient space, whatever) and so RSS Bandit should show an icon indicating that there is an attachment but that it isn't on the user's local machine, so that the user can know and choose to initiate a manual (re-)download of that attachment.

For automatic downloads, go with the TV DVR model:

1. Allow users to set a maximum upper bound on how much disk space RSS Bandit uses (absolute N GB or relative N% of volume).

2. Allow users to mark each feed as "keep until I delete", "keep until I 'watch'" or "keep until space needed" (the default). The meaning of 'watch' (or really, consume the content) in the context of an RSS feed might be a challenge to define -- you might need separate "keep until I sync to my mobile device" and "keep until the parent item is marked as read" options.

3. Allow users to prioritize the feeds they subscribe to, so that when there's a conflict for space, you can choose. Auto-assigning a default priority scheme is easy (new feeds are lower pri) but you could also chart new territory by auto-prioritizing based on user attention.

4. Expire content from the cache according to the above two rules. That is, download everything you can; free up space (according to priority rank) when necessary; and fail to download new content when no space is available or can be made available.

5. Show cache usage on the main reader window. Use color and numbers (e.g., green/yellow/red when there's plenty/little/insufficient space remaining, and show percent full).

I'll second Michael Brundage's suggestion. Best idea.

You should look at the way that JRiver Media Center handles podcasts -- there are options for "Download Last x Number", Keep up to x mb", or "Keep Laser x No of Podcasts" -- the size of the files doesn't matter as much as how much total space is being used. One 2000mb file or fifty 100mb files are equally as annoying to be automatically downloaded.