Here is a cool thing I discovered recently, and please forgive me if it is already common knowledge. There is a little hack for getting RSS feeds for tags on YouTube, and it goes like this:
http://youtube.com/rss/tag/randomtag.rss (where randomtag is the tag you want to aggregate)
Here are two examples of this tag-based feed. Andy Rush has put together some very cool screencasts for UMW Blogs which are appropriately tagged umwblogs. So, when you include http://youtube.com/rss/tag/umwblogs.rss in some kind of an RSS reader or aggregator you get the following:
Username as a Tag
What’s more, if you want to aggregate by a user on YouTube, you can just substitute their account username for a tag (seems that YouTube treats the username as a tag). For example, http://youtube.com/rss/tag/jimgroom.rss will bring the latest videos from my account.