OK Robbo I'll start ya on this one...
For me it's "both", live for today because let's face it none of us know if we've got a tomorrow.
BUT plan and prepare for tomorrow otherwise you'd never achieve anything and that allows you to keep living for each today as it comes.
The balance I think depends on us as individuals and how much we need to plan and influence the future and how much we need to be able to go with the flow.
For me in real life this at the moment translates to still doing motorsport although we're skint. Yes realistically we should be staying home with the lights turned off to avoid incurring more debt. But for me life is for living and I'm going to do the things I want to do but perhaps we'll do them differently, we'll camp more and eat out less but we're still going!!
My mum died aged 48 and that has always made me realise that you never know how long you've got on this planet and you should make the most of every day that you have. This doesn't have to be in a big way - I've never had the urge to travel but some do. For me it's about appreciating everything to the full, each sunrise you see, each clear frosty morning, the smell of coffee, the sound of the old porsche the guy opposite owns, the sound of the start of a GT race
If you've got a dream and it's something that you can achieve then go for it, the reality is that most of us will make it to old age and whilst we need to have made some financial provision to be able to enjoy the last part of our lives as best we can - I'd like to be sat in a chair at 80 remembering the things I did earlier in life - sitting in the trees at Spa above the Bus Stop in the middle of the night of the 24 hour, seeing the sunrise over Dunlop at Le Mans.
I guess I'm lucky, my dreams are quite low level, happiness, health and motorsport! I achived my ambition of going back to uni as a mature student and studying law, I qualified as a lawyer last year and although I'm carrying shed loads of debt from it the satisfaction I have of having achieved it is great.
Hope this helps

edited to say...rats beaten to it, must type faster!