*This is for the PC version, I have not played the others*

1: Do not become a vampire!
2: If you do, get cured
3: If you somehow do become a vampire and end up unfed and with your vampirism maxed, you are going to have to find a house at night where people are probably asleep. Press the ~ key to open the console, and type "TAI" to disable the AI before you enter the house. Only then can you feed. Invisibility does not work and when you enter a house everyone is going to wake up instantly and chase you down to try and kill you. Occasionally you will get lucky in a large building with multiple beds, but it is NOT worth the effort. Anyhow, the buffs are very weak, there is little plot or roleplay element to it, and its a major hassle with the bugs in place. I got cured.

In the previous games you were granted some nice stat buffs and there was more roleplay elements involved. Not to mention you could feed at will, even with vampirism maxed. In this game though you get some serious debuffs during the day, weakness to fire, and no real buffs other than some dinky spells; one of which doesn't work (invisibility). You fast travel somewhere, realize its day, then wait until night to avoid being debuffed or running into a dragon during the day (debuffed + weakness to fire = ouch). Then since you did some extra waiting after your fast travel you really need to find a place to feed. Take my word, just don't do it unless you really really want to role play a vampire.