If the main application is running, the update will happen 3 feeds at a time (which uses quite a bit of CPU, but should be fairly fast). If you update in the background (through command line, or through the widget), it will only do 1 feed at a time, and uses the "nice" command to stay low CPU priority.

In the file rss_sqlite.py, class Feed, function updateFeed is where all the action takes place (note that this runs as threads, so you might need to flush stdout if you want to see the messages when they're printed). If you need any help in troubleshooting, feel free to contact me by private message.