They do not filter out past data.
The only way to filter past data is either through report level filtering or advanced segmentation, and those are obviously temporary. (And neither provides IP-level data that might make it easy to filter out your own visits.)
Since profile filters do not filter past data, I generally recommend that people apply new filters against new profiles, and leave their old data unfiltered; it provides a better apples-to-apples comparison (since you'd otherwise be altering your data collection method mid-stream), and it reduces the risk (since if you mistakenly misconfigure your filter, any mistakes are irreversible, so better to keep an original copy of all of your data, just in case).
I'd also caution against spinning your wheels in an effort to filter out your own visits. Google Analytics isn't about collecting scientific data; its about getting trends out of imperfect data to help you make decisions about your site. You don't really gain much from filtering yourself out, but you do create a maintenance issue for the future (since you'll now have to monitor your IP addresses to make sure you're still filtering out the correct IP address.)