Anyone become a vampire or werewolf yet?
I became werewolf quite near the beginning of my playthrough and I´d say you really don´t loose anything if you become one, at least.
Unlike in Bloodmoon, you don´t transform automatically into werewolf at given time, in Skyrim it´s a one use per day power instead (the one per day restriction can be alleviated via a side quest), which lasts for 3 minutes and can be prolonged by feeding on corpses.
Along with it you get two passive effects which apply to you whether in werewolf form or not - one is disease immunity (which doesn´t work 100% reliably - I got at least one disease since, but given how long I´ve played the game it´s a non-issue) and you can´t get the well rested bonus for sleeping which is supposed to be a con, but since I don´t want to level too fast anyway, it´s not one for me.
Can´t comment reliably on how well the transformation performs in combat - it´s third person-only which is quite a deal breaker for me - but judging by the few times I´ve tried it, I think it has some situational uses. Fast running speed may come in handy in some encounters, the leap power attack deals a good amount of damage and the form has a roar ability which may scare enemies.
One thing to note though, the applicability is also limited by the fact you can´t use inventory or cast spells while in the form and the only way to heal is to feed on dead bodies.
It doubles your health I believe,.
It increases health and stamina by 100, which is one of the reasons why it´s only situational, even more so on higher difficulties.
I´ve noticed that killing people in werewolf form doesn´t net any bounty so it may also come in handy in some Dark Brotherhood quests, for example.
As for whether it can be cured or not:
As I see it, you get immunity to diseases and some possible situational uses at zero maintenance
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