Did the same and picked up a pinhole cap for my Mamiya 645. Just got a roll back that had a few exposures on it and I can see that more experimentation is in order, but I did get a couple of interesting exposures. I think with a pinhole the subject matter and especially the framing are very important. To me it seems, just from this roll, that you need to concentrate attention on less subject matter then more. My pinhole landscapes were no big deal, seemingly just misfocused frames whereas cropping the image down and concentrating on less subject matter imparted more of an ambience to the image.

Here's a link to a resource to determine exposures for your particular pinhole size. Print it out and carry it on you. http://www.mrpinhole.com/calcpinh.php