I'm wondering if there is any way that i can check up how many social sites have I registered or submitted to?
Log your referers, check google webmaster central .. you won't find it out by magic in future write the urls down in a textfile, you'll need it anyway
When you are making new logins or doing the submissions, that's the best time to put this information in an excel sheet However, you can still check your backlinks in yahoo, many SB sites won't show up because they use a 301 redirect from story page.
if you didnt keep record while you were signing up and submitting, then there is no easy way to know. you can look for your backlinks using yahoo site explorer or google webmaster tool but you will not get the exact number as some social bookmarking sites are nofollow
I use this one for my submissions in digg, technorati and one more. http://tools.khrido.com/webtools/social-bookmark-checker.aspx