Actually you can tell a rather noticeable difference it really helps recovery....
here is a little clip from a site summarizing some findings:
Vitamin C: This vitamin, mainly known for it's anti-oxidant properties, may also have some anti-cortisol effects. A study done by Stone entitled "Effects of Vitamin C on Cortisol and the Testosterone: Cortisol Ratio" showed a decrease in cortisol levels in 17 junior elite weight lifters. This study also showed that the individuals taking Vitamin C (an extra gram a day) improved their testosterone:cortisol ratio by over 20%. This type of decrease in cortisol can lead to increased muscle and connective-tissue hypertrophy and enhanced recovery from training. Since Vitamin C also decreases your chances of suffering from a cold or flu infection by 30% (14) and may aid in collagen synthesis, it would be wise to take some extra vitamin C when involved in an intense weight-training program.