I have a web app that stores the locations of farms in West Michigan. You can search for a product (e.g. "broccoli") and it will show you all the farms that grow that product.
Right now I'm using MySQL and using trigonometry to calculate the difference between the user's location and the location of each farm. It's not a bad way to go but it did take some doing.
Another thing I want to do soon is to map out growing seasons for different products for different regions. (For example, I want to show that avocados grow at a certain time of year in California but never Ohio.)
I realize this is an open-ended and possibly naive question, but might it be worth it for me to make the switch to PostgreSQL/PostGIS to take advantage of its spatial capabilities?