This is actually nice, and will prove handy for me. I tend to use a lot of characters when I post, so having an even smaller url shortener will help me make the most out of limited space. Not to mention the site is aesthetically pleasing and seems fairly simple. Kudos!
(Side by side comparison)
PS: I tried using hi4.us a couple of times, and 1/7 of the url's I attempted brought me to a white screen when I tried to follow the shortened url. You may wish to look into this, though I am sure it is nothing more than me putting in an erroneous url.