Cats do their own thing in their own time. About 5 months ago I got a very timid girl (whom I named Snicker) from a friend who owns a shelter, this cat had been there about a year and wouldn't come out of her shell. When I got home with her she immediately hid behind the couch, but my little fella Roscoe (maybe 4 months old at the time) knew something was different and wanted to play.
I'd lift up the couch every time I walked by and pretty soon Snicker decided to hide under the bed instead. Roscoe would spend time under the bed too, and surprisingly I never heard any growling or hissing from either of them. Within a few days she was coming out when the lights were on and I was around.
Snicker and Roscoe soon became best buds, they were always playing.
http://youtu.be/HOoG1pgyHoc (don't know why this won't link)
My big goofy boy Domino joined in as well, and now he can't get a break from them. He's very patient, though, and has never gotten angry with them. The other 3 girls are ambivalent at best, and Snicker isn't shy! She's bitch-slapped one of them for looking at her the wrong way before LOL.
Snicker has made herself a place in the home, but even now I can rarely touch her. She trusts me enough to sleep on my bed from time to time, and will do the slow blinking thing at me, but runs when I try to touch her. If she's rubbing up against either Domino or Roscoe I can pet her, though, and even pick her up. If she looks and sees it's me holding her, though, she wiggles free and takes off. The important thing is she has a good home, I don't care if she never becomes snuggly or cuddly.