In fact, Marc from Mojang is asking for suggestions on what players would like to see if seasons are implemented in a future Minecraft update. Here are a few of the ideas they've come up with so far.
- Grass with a certain light level has a small chance of randomly spawning a flower, and certain flowers are only available during spring.
- Higher chance of rain
- Lower chance of rain
- Lower chance of snow in taiga and tundra biomes
- All villagers wear sunglasses
- Leaves on trees change to autumn (orange, red, yellow, brown, etc) colors and can be collected as blocks of those
- Piles of leaves can spawn under trees, and could stack up in piles like snow. These could be collected and crafted into leaf blocks like you'd get from a tree.
- Chance of snow in any biome during winter
- Small lakes have a chance of freezing
- Slightly higher chance to spawn wolves, and/or small chance of wolves spawning outside of their natural biome, if it's snowing.