My study of church history and doctrine has thus far led me to believe that Protestants, at least the more conservative denominations I am familiar with, while professing to believe in Sola Scriptura actually adhere to a form of Tradition (called "single source tradition" by McGrath). This type of Tradition is essentially just a specific way of interpreting scripture and doesn't allow for anything that can't be supported by scripture. However, it doesn't allow for the willy-nilly interpretation of scripture.
The churches I've been in have typically claimed that scripture must be interpreted in a certain way, and have condemned taking scripture out of context or twisting it to conform to novel ideas. This sounds a lot like "single source tradition" to me as I cannot think of a reference in scripture that speaks to how scripture is to be interpreted.
As this is only the beginning of my study on Church history and doctrine I could quite easily be mistaken. However I cannot assume Sola Scriptura anymore. I must be able to prove it to myself, especially seeing how it appears to me that most churches that profess Sola Scriptura do not actually practice it.
So, dear studied Protestant friends, if you have a defense of Sola Scriptura, I'd be happy to hear it in the comments below.
... Okay fine, Catholics can comment too. But only if you're nice.