If you speculate on patch notes you will remember dream shards looked like a good investment. At the time the only thing they were used for were to learn new enchants. The upcoming patch notes said the existing enchants were going to be changed to use more of them. I bought them like mad and I advised my friends do to the same.
8.5-11G is what I paid for each one and I ended up with well over 300 shards. I think lots of people picked up on this and I know several blogs covered the idea. So after a huge spike on patch day the market crashed. The price settled at 13G. Not much of a profit. I decided that everyone had a huge stockpile and was watching the market.
I walked away for a few weeks. The new price was 15-16G each at this time so I would sell a few here and there. for the most part, I held onto my inventory.
The next patch came and it also should have increased shard prices with Ulduar release, Again people were thinking about shards and the prices stayed low. So gain I held onto most of my shards.
By now I was getting a little more aggressive in selling the shards. I would post them in stacks of 3 and 6 a little over market value. I could also catch the market when it would shift up. This didn't happen often and when it did, the market would crash by the end of the day.
About 3-4 weeks after the patch, the value of shards started to clime. Once they got up to 25-30G I started to liquidate what I had left. I still had 200 shards at this point and they ended up creating that huge profit I was looking for. It was just a few months later than I expected.