Just a few things to note.
1) Glyph of Outbreak is amazing when coupled with the talent Plague Leech. Because the glyph remove it's cooldown, it translates into 2 free Death Runes every 25 seconds (Plague Leech CD). Without Glyph of Outbreak, your Outbreak has a 1 min cooldown, which means you get the 2 free Death Runes every minute instead of every 25 seconds (waiting for Outbreak to come off CD before Plague Leeching). In addition to this, Blood DKs generate RP in insane quantities, so a glyphed Outbreak essentially becomes spammable.
2) If you're tanking a dungeon/raid or anything with other people, do
not pull with Outbreak. It applies your diseases but does not DoT tick on it's initial application. Hence, you run the risk of having DPSers aggro the boss on pull and getting one-shot. With that being said, initial pulls should always be done with a taunt or an Icy Touch+Plague Strike combo because those abilities do damage on contact, thereby gaining you threat.
If you'd like more in-depth stuff, check out Troxism's guide:
http://sonofalich.com/forums/viewtopic.php?f=21&t=51