100% loans are OK in certain circumstances. One example is if you have cash but would rather keep your money in the bank for a rainy day, or investments, etc. This way if you do get in a bind, you can use that cash to either get by, or pay down the loan to sell it if values have declined.
Another one is if the property is legitimately being sold well below market value. Where you have trouble is buying at 100% in a soft market, or on a very high end home (high end homes fluctuate in value much more than more modest ones do) or when you don't have a dime in the bank to fall back on.
My story is the same as yours...sold the house almost two years ago just at the top of the market. The people who bought our house only put 5% down! I couldn't believe it. Since then the house has definitely gone down in value, that much I'm sure of. We took our profit, bought a new home free and clear. It's great not to have a mortgage!