It works really well. To enable it, you click a link on your desktop website home page and are presented with a list of available topics (everything from here). You check a few boxes and click 'Save', and from then on a set of checkboxes marked 'Topics' will appear under the 'Categories' line when you want to make a new post. Check a box and make a post, and it will automatically be syndicated up to the Topic Exchange. Great!
PyDS is an open-source clone of Radio Userland (the software I use to edit this weblog).
Spanish-speaking folks are using a blogchannel to build the directorio_blogs_hispanos (introduced here). Another pretty active channel is Austin blog. If you have a topic close to your heart, by all means go ahead and make it a channel! You never know who's going to show up!