After a week worth of worrying and patrolling my city's I have completed both sides of the story and as far as I can tell both saved games have been without inccedent for 3 real life days. I have done everything from fast travel between towns during the day and night,waited in every town till dark,went in and out of shops.its safe to say that the main story completion seems to be the final nail in the coffin of random attacks.as time goes on there are starting to be posts on diffrent forums that are also experiencing this.so I urge you to try it out,and avoid the main city's until you do(it's possible on both sides of the story to never step foot in towns during the main quest).come back here and report your fidnings when you finish so we can maybe get a full account on other peoples saves and not just mine..there is light at the end of this genocidal tunnel!
On a side note,on the dawngaurd side save, I completed the companions quest and also never once had an attack occur while going in and out of whiterun doing and turning in quests.(about a month or so of ingame time

I still get attacks even after finishing the dawnguard side of the mq

How frequent?

To be honest I haven't had any since I completed the quest nd I'm trying to find them

I'm starting to think it works like any other glitch some people are stuck with it and others aren't.kinda like glitches like the "blood on the ice" or things like that.where not all have that issue just comes down to being unlucky I guess.
Which would explain those people who think its cool or shoot others down for wanting it fixed...there not getting the full force that the glitches ones are experiencing

Glad I play on pc.But I will keep this method in mind if they haven't fixed it on release for us.

After finishing the Vampire side of the DLC I've experienced no attacks.