I think if you can practise on a grand piano, go for it! Otherwise I think digital pianos are fantastic, better than a not-so-good upright, IMHO. Here are some pros for digital pianos;
1. You can practise anytime you feel like, even at odd hours while wearing headphones.
2. Digital pianos are always in tune. You never have to pay for a tuner, or discover you've been playing an out of tune piano which can really screw you up.
3. You can easily record yourself, you just plug into Garage Band, and record and you don't have to worry about things like hiss and ambient noise which can make other recordings sound like crap.
4. You can plug it into a computer and use programs such as Garage Band, Finale, and Band in a Box, to create your own music, compose, print up scores, record midi, endless things you can do.
5. you can play songs using different sounds such as harpsichord, guitar, etc. (Makes boring scales more fun.)
6. A digital piano can fit into small living spaces easier than a regular piano, especially grands.
7. A digital piano is portable, thus you can easily take it on gigs, or over to your mom's to play her some songs you've been practising. Or take it with you when you travel so you can always practise and not get behind.
I have a digital piano, and I love it, and I'm planning on getting a decent baby grand or upright when I save enough money. I think it would be great to have both, because I love what you can do with the digital on the computer, especially when writing tunes. The baby grand would be awesome too, and I think it would help with attracting students for lessons, because they'd enjoy playing on a baby grand, and help pay for it, these plans are for the future, one or two years from now.