That may have been ground down by the big ice cube, or it could have been one of Joe or Scott's practice rocks. 

Rocks can be rolled along the sides of or in front of a glacier or ground flat underneath them.

Thanks for the pic, farmdude. That flat surface certainly does look "lasered"! It is amazing how straight and flat it is!
But I don't see any manually "ground" surface on it. The wear on the flat surface all seems to trend in the same direction so I am going to have to agree with Scott that it is a "geofact" or "glacial erratic".
A great example of how nature, in this case a glacier, can alter rocks. These "geofacts" are often utilized by man since they are all ready suitable but I don't see any "use wear" on this stone.
We don't see examples of this down here, so it is very nice to see such a good example.

Here are a few pics of an artifact hammer/grinding stone for comparison. Note, if you can, how smoothed the bottom ground surface is. The sides of the stone were for percussive hammer like strikes which eventually wear the stone into the overall round shape and there are a few Plow-strikes evident. Pic 1 is top, Pic 2 bottom, Pic 3 side.

Ya know, farmdude, rocks like this and a lot of "ground" rocks in general are a real hard call, and I, just looking at a picture, am in no position to say for sure one way or another.
Lots of times you have to look at it with magnification. Maybe you can see how it was made or ground?
It also makes a big difference if you find these in an area you are seeing other artifacts or not. That would increase it's chance of being utilized. Sometimes natural formations have been utilized making it a little of both. Often highly finished objects were inspired by their natural shapes.
My rule of thumb is; "If it is one, you'll know it." Meaning, if it is an artifact, and has been used, then it ought to have been used enough for you to plainly see that. 

I'm thinking geofact for this rock but would be happy if you found out otherwise. 

Thanks for the interest Joe. It doesn't bother me if it's a geofact. I think it's just as cool if an interesting rock was formed by a glacier rather than early man. I just think its neat to post my finds to a place where someone appreciates them like I do. Here's another geo/artifact.

Hey farmdude, I don't know if you're still checking in or not. I know we weren't much help.
But I found a couple good examples of why it's hard to jump to the conclusion that these weird geofacts were the product of human activity.
There is nothing new. Nature has all ready done it all!

There are several famous "split-rocks" around the world. Here is a link to one in New Zealand.
https://en.wikipedia.org/wiki/Tokangawh%C4%81_/_Split_Apple_Rock

And here's an example of what nature can do from the Colorado School of Mines Museum.

awesome. thanks for the tips guys. I will keep an eye out.