Dawnguard

One should be very careful when playing with Dawnguard installed on account of the random vampire attacks in cities and towns which can result in the death of someone you'd been thinking of marrying.  Anyone who is outside at the time of an attack is likely to rush in to fight the vampires, and also very likely to be killed if they do so because they don't have the skills or health needed for combat.  If you are ever near a town or in a city at night, or late evening, be careful and keep your ears out for sounds of combat and get over there as quickly as you can.  It's also a good idea to save before exiting any buildings at night, and to fast travel to the outsides of cities to make sure you enter them during the day time when an attack is much less likely.  Unfortunately, though this has mostly worked in my experience, I have in fact left a city with everything looking fine, been away a few days and then fast traveled to the stables, waited there till morning and then entered - and found the remains of a deathhound and an ash pile by the gate.  It doesn't make any sense that this could have happpened while I was gone since essentially that section wasn't in existance since it wasn't loaded, but.... I can't deny the truth of what I just saw.  I didn't see any bodies of townsfolk, luckilly, but still.... it is unsettling.  So if you want to make sure your potential spouces stay alive, be very very careful and save often.