My 06 team had a scrimmage today against a local team. It was their first time playing in our 4-3-1 formation. It was nice to see that it had only a minimal effect on our style of play. We still looked to circulate the ball with short passes, and pressure immediately upon losing it.
Some of our attacking movements were off, which is to be expected. It's still refreshing to see that the repetitive work done in training isn't instantly lost as soon as a small aspect of your play changes... and also serves as anecdotal evidence that formations are not 'tactics', merely a tool.