Were they sort of blackberry -like in shape? I'm just guessing maybe young mulberry trees, but I don't know at what age they start producing fruit. Seems like they might be fruiting now though. If you don't know what mulberry trees look like, Google mulberry tree, picture.

It may also have been a Pokeweed plant - they can get quite tall. If the fruit looked almost the same shape as a bunch of grapes ('though much smaller and not on stems) then it may have been pokeweed. Double check as poke is toxic. It's a perennial weed, spreads prolificly from seeds, which the birds love.

A photo, including a good shot of a leaf, would help in IDing.

You guys are the BEST!
Yep, I think it's pokeweed. Looks like you can eat the leaves (no thank you) but not the berries.

http://waynesword.palomar.edu/ecoph24.htm

Robins absolutely love the berries of the pokeweed, so I leave a couple of them out near the woods every year even though they're such an invasive plant. I even think they're kind of pretty...

My MIL cooked up some pokeweed and fed it to me with some other greens, but from what I've heard, that's an old practice of questionable wisdom because it does have certain medicinal properties. I don't remember what they are. Some people have a slight allergic reaction from touching pokeweek. DH just pulled some of it up from our backyard this week.