How bad is a code base really? That's a hard question to answer. An easier one is: if you jump to a random place in your code base, how often are you embarrassed, horrified, happy or impressed?
This tool might be useful to you if you're considering taking a job working on some existing product. Ask to run this a few times with a developer so they can explain what the code does and why. Looking at the face and listening to the noises the developer makes will probably give you a strong indicator if this is a place you want to work at :P
Download random_place_in_code.py and run it. It'll open with vi by default, but it also takes an argument mate to open the file in TextMate.