During my current game I noticed a few DB Quest related things that probably should be fixed:
http://www.uesp.net/wiki/Oblivion:Accidents_Happen
- None of the items in Baenlin's house are marked as private property, and will not be marked as stolen if you take them.
This is probably to avoid problems when his nephew Caenlin moves in. Don't know if a fix is possible, but would be nice if it is.
http://www.uesp.net/wiki/Oblivion:A_Kiss_Before_Dying
When you go to pick up the dead drop you can jump through some bars.
http://www.uesp.net/wiki/Oblivion:The_Coldest_Sleep
Now that business has been taken care of, you should head for Nornal to collect your reward/next contract. The ruins are filled with rats, crabs and marauders, this doesn't change if you're higher than level 5. Upon entering, head down the stairs and take a right. Dive under the water and swim towards the door. It's locked. There exists A Rusty Key, that opens the lock, if your security skill isn't that high. However, an alternative way of entering the room is to use a potion or item that gives you "Water Walking on Self" and walk through the iron bars above the door, effectively bypassing the gate. In the chest is your gold and your next contract. You could also just jump out of the water to get over the gate.
Also, a Thieves Guild related:
The http://www.uesp.net/wiki/Oblivion:Waterfront_Tax_Records that appear in Dareloth's House after you complete the TG quest line, is the wrong one. It is still a Quest Item.