One item I mentioned in terms of custom aggregator code might be parsing the post (or the content located at the post's link) for microformats. Microformats are basically a way to embed semantic information or structure into web pages within the existing tool of HTML. Microformats can provide additional structured information about people or companies (hCard) or events (hCalendar) or reviews (hReview) or locations (hCard again) that are contained in the web page, or they may provide additional metadata for the current page - the providing a set of words that describe the page ("technorati" tags or rel-tag) or the license under which the page falls (rel-license).
If the feed provides an HTML version of the content (type="html" or type="xhtml", or just by convention), it may be that there are microformats in that HTML. It may be that only the text is available, and then you have some decisions to make as to whether to get the information from the link given in the feed for the post. There are some trade-offs here - you can't be sure which data on that page has to do exclusively with the post (for example, there may be data in a blog roll that is on every page, and doesn't have to do with this post in particular).