Let me use cars as an analogy. If you have been taught to drive only using an automatic gear car and I suddenly asked you to drive a car with manual gears, you would have great difficulty.

However, all the F1 racing cars on the Sepang circuit have manual gears simply because the drivers can get the best performance out of their cars using manual gears.

I would advise you to continue using a P&S camera until you realize its limitations, then that is the right time to get a dSLR. I would think 90% of holiday snapshooters would never need a dSLR.

Having said that, there is no valid reason why you cannot use both. I carry along my Canon Ixus and my Canon 350 all the time.