I went to Proof on a Saturday night as it was the venue selected to host a charity fundraiser. For this reason, I'm not sure if the night I went can be described as an average night for this bar.
The place itself has a nice layout and ambience. There is a DJ and a large patio, and plenty of seating. The patio seemed a little lacking in terms of heaters though.
The drinks range from $12 to $14 a cocktail. This is double what you would pay at any average bar, but considering you're in Yorkville I would say it's not out of the ordinary.
The one annoyance I had with this bar is the bartending service. It was abysmal. The bartenders looked confused and were painfully slow. For a bar that was half full at most, I had to wait 20 minutes just to be noticed. The bartenders would even leave the bar to go to the back room for some reason. It just seemed very disorganized; I felt like I was at an upscale lemonade stand at the CNE.
Overall, the nice layout did not make up for the lack of service. If you have the word "Bar" in your name, you should be capable of living up to it.