Mark and I have been frequenting the local farmers markets where we live for a little while. Last year, the one by the Food Lion in Columbia was our preferred location, now it is the one under the 83 viaduct. (Saratoga St. between Holliday and Gay) It's from 8am to 12pm, running until December 21st.
The bigger question is probably why do we go to the farmer's market? Honestly, the main reason is not because we want to support locally grown produce or organic farming. The main reason is because our local grocery store's produce section sucks.
The relative difference is obvious - the farmer's market in Columbia was small - usually three or four produce stands, a bread stand, and one or two flower stands. There were usually about 10 customers at a time, more in the spring. The Baltimore farmer's market is huge - probably at least 10-15 produce stands, plus that many or more food vendors, local artisans, handmade dog biscuit sellers...it takes up an entire parking lot and is filled with people. The Baltimore Farmer's Market is like the Riverdale Farmer's Market on crack. There is a donut vendor here too, but the line was way too long - there is an advantage to a smaller farmer's market, sometimes.
I highly recommend checking out the Baltimore farmer's market, and if you don't live in the city, check out this - http://www.mda.state.md.us/md_products/farmers_market_dir.php - to find your nearest one.