I think Tiagra is a really good groupset. It's better than Sora because of the paddle shifters. With well cut cable housing and a good tuning, Tiagra works pretty nicely. Everyone wants ten speeds, but how much faster is that extra gear going to make you... Not everyone thinks SR 11 is better than DA or Red.

I used to have a 2008 Cannondale CAAD9-6, which had full Tiagra. It was alright, but I doubt I had it tuned up perfectly. I recently swapped bikes with my friend so he could try mine. His bike had a Sora/Tiagra mix and I was actually surprised how well it shifted... even under load. I did the same with another friend who had Sora/Tiagra on his bike and I was just as surprised.