I'm using Google Code to host my application code, its conveniant and the SVN repository means I don't have to worry about backups
When you create a project on there you need to select a license, I chose GNU GPL v3.
By doing so, does that prevent me from selling my application on the Android market place?
No. It just means no one can distribute your software without including the source or an offer to send the source.
You should really read the license before you choose to use it...
It doesn't prevent you selling it, despite the license you still own the code and can issue it under whatever licenses you so desire. It does mean that anyone can take your code, compile it and install it on their Android without paying you a penny but that's probably a small portion of those who might want a good app.
Many people believe that the spirit of the GNU Project is that you should not charge money for distributing copies of software, or that you should charge as little as possible — just enough to cover the cost. This is a misunderstanding.
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Distributing free software is an opportunity to raise funds for development. Don't waste it!
To Wooble's answer I'd like to add that the GPL not only guarantees that people must (offer to) distribute the source code when distributing your program, but also that any changes they make must be compatibly licensed if they distribute the changes in compiled or source form. This latter part means that if someone else builds on your work, say by making their own app, they have to share it with the world under the same terms as you do.