I took lessons for about 5 years while I was growing up, and for that period of time I could definitely say I knew what I was doing. Now that I haven't had exposure to a piano in at least 4 years I no longer can claim that. I still remember how to read music, which in turn allows me to 'play', but it's definitely not as natural. It's like anything; without constant practice or attention to the skill it kind of disintegrates. Now when I play I need to have music in front of me so that I may read, and even then the notes seemed labored and sluggish.
If you want to learn, the biggest hurdle is reading the music, but if you stick to it, learning to play past that point should be a breeze!