Which phone do you have? On my iPhone4 it lags and is slow all the time. I think particularly when it's in air plane mode but it might just be my perception.
Same here, I'm on an iPhone 4. Apparently it's just constantly pinging the server when you launch it, even in airplane mode. You'd think it would know to skip that. Will certainly be testing it out on the iPhone 5 when I upgrade next month.