No, the antenna is pretty much omnidirectional. The main difference is your body's effect. (although, there are other materials which will block RF, too)
I've always been pretty amazed at how well (?) they (cell phones in general) work when used up against your face. I have noticed some improvement, though, in phones that have antenna in the bottom (like the iPhone), which generally put it farther away from your face (it usually angles away at the mouthpiece).
edit: you probably will realize the same improvement if you are using a headset, and lay the phone down away from you (for instance, on the armrest of your chair). The signal at my home can be a bit flakey at times, so if I'm on my BT headset and put the phone in a "sweet spot", everything's fine. Note to iPhone fans: This probably isn't saying much, but the iPhone is MUCH less sensitive to low signal levels than my RAZR was. I haven't needed to worry about where I place it.