A key part of "Understanding Your Data About Yourself" is that it's your data. So, if you've used UYDAY and put a bunch of data into it, you should be able to get your data back out. Available under prefs is "Download data" which gives you a CSV export of your data which should be usable by many common tools like your favorite spreadsheet or scripting language.
It's not perfect yet. It only returns the most recent 1000 entries unless you manually edit the URL There are probably better formats than CSV. But, we hope this is a good start to showing our commitment to helping you manage your data.