In the past month or so I have been using the Dvorak keyboard layout along with the Qwerty layout although the ratio of my Dvorak to Qwerty use has increased over this time. I'm nowhere as fast typing on Dvorak than Qwerty so far but I hope to get better. So I went into learning Dvorak with little idea how it would fit in with my existing typing skills and I had a one main question (or perhaps even a worry). Would I be able to type in both layouts much like someone who is bilingual where they can be fluent in both languages where learning a second language would not diminish their fluency in their first language? I have not become experienced enough to answer that question though I can still type in Qwerty but I make more typo's than I used to. Mostly I seem to sometimes get just one key mixed up. I'll repost when I have a more definitive answer.
Though there was another main thing I wanted to get across in this post. Using the Qwerty layout I would usually type by remembering not only where keys were but by the sequence of keys for common letter sequences, hence whilst I can type any word I am even faster at particular letter sequences such as the, them, they, etc... any common short word. I'm guessing most people are like this. After you've been typing for a while you learn where the keys are, but you also learn key sequences for common words. While I was learning to type in Dvorak I went through several stages. At first I would just look all over the keyboard for the key and then press it. Then gradually I began to know where the common letters were (those being a, o, e, u, i, d, h, t, n, s) so I didn't always have to look for these ones. This is the stage I am at the moment. Once I can become faster at these common key seqences I should be all set, at the moment I am beginning to notice this for "the" and "rea". Practices makes perfect, though I will try to not loose all my Qwerty layout skills.