I have a fancy printer that does 13x19 prints and I love it. I can look at my photo's all day online or on my computer at home but seeing them big and printed out is so pretty. Of course 4x6 is nice and convenient and easy to get from any drug or food store.
I print out a lot of my stuff but I don't have any of it on my own walls in my apartment. It's odd, I love giving them out as presents to family and friends. What I have on my walls now is "Squid" oriented art that I have purchased on the internets, mostly from Etsy's.
BUT, today I saw something of mine in a local paper mag that prints up a Guide to Portland Magazine once a year. It's about a 5x7 photo and it looks really good, I think it's ok when I look at it on flickr and right here. But it looks really good in the mag, maybe because I got paid for it but if I can give you advice, print your work, LARGE. Unless you take crappy photo's it will look good printed up.