I think a useful feature that should be simple to implement is a time offset. I'll explain myself:
i have many blogs on my site aggregated using aggregator2.. the posts are sorted by posting time. The blog time that is (as opposed to the time it was aggregated). The problem is that i have blogs from different areas and different timezones.. so a blog how is 2 hours ahead of the others will have it's posts stay ahead of other posts from other blogs eventhough they where posted after it..

for example if a blog in NY posts at 10:00 am (EST).. and at 9:00 am (Pacific time) a SF blog posts, due to the time difference the NY post will remain before the SF post..

The solution would be to add a time offset variable to each feed. in the example above, setting a +3 hours offset for the SF blog will automatically add 3 hours to the blog post.. hence all the feed items will be ordered by their real posting time..