MythNetTV is an early but effective MythTV extension that downloads podcasts and adds them to your recordings list, just like the free downloads feature on TiVo (except you can subscribe to anything you want, provided the format’s supported).

These commands will install and configure the app (be sure to substitute the path you want videos saved to):

sudo apt-get install mythnettv
mkdir /your/dir/here
mythnettv --datadir=/your/dir/here

Subscribe to some geeky shows:

mythnettv subscribe "http://revision3.com/pixelperfect/feed/Xvid-Small" "PixelPerfect"
mythnettv subscribe "http://www3.youtube.com/rss/global/top_rated.rss" "YouTubeTopRated"
mythnettv subscribe "http://revision3.com/trs/feed/Xvid-Small" "TotallyRadShow"
mythnettv subscribe "http://applebytepodcast.cnettv.com/" "CnetAppleByte"
mythnettv subscribe "http://buzzreportpodcast.cnettv.com/" "CnetBuzzReport"
mythnettv subscribe "http://cnetnewspodcast.cnettv.com/" "CnetNewsDaily"
mythnettv subscribe "http://firstlookpodcast.cnettv.com/" "CnetFirstLook"
mythnettv subscribe "http://hackspodcast.cnettv.com/" "CnetHacks"
mythnettv subscribe "http://howtopodcast.cnettv.com/" "CnetHowTo"
mythnettv subscribe "http://realdealvideopodcast.cnettv.com/" "CnetRealDeal"
mythnettv subscribe "http://revision3.com/coop/feed/Xvid-Small" "Co-Op"
mythnettv subscribe "http://www.onnetworks.com/feeds/1460/video/rss.xml?target=site" "PlayValue"

Get show lists for all subscriptions, then download 10 shows:

mythnettv update
mythnettv download 10

List the next 10 shows that will be downloaded:

mythnettv nextdownload 10

Download 1 show from the given subscription:

mythnettv download 1 CnetNewsDaily

List subscriptions:

mythnettv list

More info on these commands and others:

man mythnettv