After chatting with several people it sounds like there was a group of sites Bing deindexed in the April-May timeframe under the umbrella of spam. Given the industries that's probably accurate for some of them due to the need for aggressive tactics.
While it isn't exactly new that Bing would ban sites, I do find it to be a lot more rare and don't have nearly as much data on the engine as I do for Google's timeframes. For instance, in Google someone that is slapped for cloaking might be sitting out for a year, sometimes two. For aggressive links I've seen more moderate penalties that don't involve complete deindexation. What about Bing though; in the current era of Bing WMT have there been any confirmed timeframes for deindexation and reindexation after resolving spammy link issues?