If you haven't noticed, I didn't pay much attention to the 2008 election at all, so I'm unaware of how competitive Democratic primaries usually play out. Clinton has so many weaknesses that I have to wonder if the hate of her is unique, or if it would generally be applied in similar fashion to the opposition candidate(s) no matter what.
Brutal primaries happen more often than not. Consider --
1980 -- Horrible, nasty, vicious primary between Jimmy Carter and Ted Kennedy which ended in a contested convention. The Carter Campaign kept trying to make thinly veiled references to Chappaquiddick. It ended with Carter winning but unsuccessfully trying to chase Ted Kennedy around the convention stage for a handshake (lol). We all know how the general election turned out.
1984 -- Another very long and hotly contested primary between Walter Mondale and Gary Hart.
http://www.slate.com/articles/news_and_politics/politics/2007/09/remember_1984.html1992 -- Bitter personal feud between Jerry Brown and Bill Clinton which ended with Brown refusing to endorse the Democratic nominee.
https://www.youtube.com/watch?v=K5kUITklALQ2004 -- "Independent" groups associated with Dick Gephardt ran negative ads against front-runner Howard Dean with Osama Bin Laden imagery in them.
https://www.washingtonpost.com/archive/politics/2003/12/17/anti-dean-ad-is-criticized/3f44dd20-18ec-4ded-9daa-1d30e8b1e75b/2008 -- Hillary vs. Obama debate -- "Corporate Board of Wal-Mart" vs. "slum landlord business in Chicago."
https://www.youtube.com/watch?v=MD9F1t9GQzA