You can check out the list of ongoing issues for yourself over at the Gearbox forums, where the biggest perpetrator is undoubtedly the glitch that causes a player's stats to be downgraded to a big fat zero following another player joining or vacating an online match. Another glitch does the same thing, only with your entire inventory of weapons; Gearbox says the worst issues are fairly infrequent, as scary as they may sound.
As of right now, there's currently no fix or workaround for a lot of the potential game breakers, though the majority of issues aren't as bad as those listed above. Still, Gearbox is working to resolve these issues and if you've found something that isn't on the list, we suggest you hit up the technical support section. We can all make these lands a better place ... together.