I started taking creatine about 2 months ago and have loved it. I'm also a hard gainer and after getting very lean (160 lbs on my 6'0" frame) I wanted to bulk back up. It was VERY difficuly to get back to the 168lb mark, which is where I started creatine. I at first used a monohydrate (powder, most common form) and had a bit of bloating and upset stomach. I since switched to a PH-filtered creatine called Kre-Alkalyn, which uses less creatine but absorbs more into the system to the the PH-buffering.
I started a thread on it here:
http://e90post.com/forums/showthread.php?t=357697
I've since put on more weight (currently at 177 lbs) and my muscles have become like rocks. It's helped a bit size-wise but I think it's biggest benefit is how it helps me push out the last reps in any workout, or have the energy to kick out one more set when my body is exhausted. Truly it helps me push through the weight when my body otherwise wouldn't be able to.