Retailer Exclusive DLC
Perpetrators: EB Games, Best Buy, Wal Mart
Worst Example: Batman: Arkham City
As if the massive pre-order culture wasn't bad enough, most retailers have worked out special deals with publishers to get special content that can only be obtained by shopping at their store. This is great for them as a business move - capitalizing on fans who want more than the base content - but it leads to a fractured experience that says it's impossible to experience everything the game can offer unless you buy multiple copies at multiple stores or do some shifty Craigslist deals.
Most of the time this stuff is generally useless, but when they start throwing in special weapons that unbalance the game - even through the simple addition of options - then it becomes a problem that affects people who don't want to play into the retailers' hand. The irony of it all is that most of this content is made available shortly after release as a stand-alone purchase for more money, even though it's all content that was done and ready day-and-date of release.
The Solution: Offer general pre-order bonuses, but don't lock customers out.