All the people I know (all in the forums) who have gotten the ZZR as a first bike or first sportbike are totally impressed with the power of it. Out of the bikes that are available new, I think the ZZR 600 is designed to compete with the Honda CBR 600 F4i (the '06s are still in the dealerships) and the Yamaha YZF-R6S. Out of those three bikes, all of which are last generation race bikes with minor tweaks to make them more comfortable, The ZZR is probably the slowest, but the cheapest. It is also the only one without fuel injection, though that is honestly not something to get too bent out of shape over in my opinion. Because I love the red, I think the ZZR is the best looking, though I think I have seen a candy red R6S that looks really cool.
Out of the three, I think I would get the ZZR based on the looks and the price. The power will still be pretty mind blowing for someone who has not had a 600-class sportbike before. You will have no problems riding with any 600 on curvy roads, where rider skill is much more important than a few pounds of wiehgt or a few extra horses. If you get into drag racing, the bike will become a disappointment after a while, but otherwise, it should be capable in pretty much any situation. Even on the track, until you get to be a true expert and race with other true experts, you will be competitive with the ZZR when racing against other riders who are novice. The gist is that though the ZZR is statistically a bit slower than the current race replicas, it has the power to hang in pretty much every situation where rider skill can make up the difference, that being just about everywhere except on drag strips and veteran racer track racing.
Basically, since the ZZR is so cheap and actually looks cooler than most of the other bikes out there, as well as being more comfortable, I'd say it is a perfect buy for someone's first sportbike, and I personally feel it will have the power and handling to keep you satisfied even after you have gotten into some pretty serious peformance riding. You'll probably never need another 600. If you really get to be speedster, you might one day graduate up to a literberike or a dragbike, but the only time you would ever need a 600 would be if you make a career of racing middleweights.
EDIT: Also, mt CBR 600RR does have a fuel guage, but I never really use it. I still use my tripmeter. It seems the guage looks full after a long time and then shoots to almost empty almost at once. Then the last bar of fuel supposedly starts blinking when you are down to your last gallon, but you can't really be confident how long it is going to blink before you run out of gas. Basically, using your tripmeter as your gas guage is a better way to manage fuel if you ask me.