I agree with all that Alexedge has said and he obviously knows a lot more than me, but if you're thinking of alternatives, one of our staff is a novice rider, and has a Yamaha YZF600 R6. It's IMO sportier than the CBR600 and carries his girlfriend regularly but may be not quite as good an all rounder as the CBR600. If you don't want something quite as sporty, but still fun, either the Suzuki Bandit 600 or Honda CB600 are both IMO good bikes
The R6 is a fantastic bike, I fell in love with it's telepathic handling when we first tested it in '06, and it killed the competition in our '06 600cc shootout (http://www.motorcycledaily.com/23june06_supersport.html
) based again mainly on the chassis. But as I've told quite a few friends, it's really a bike designed for experts, and it's extremely
track-focused. Little to no low-end and mid-range power, which makes it sort of a bitch for around-town riding.
I speak from experience - after the shootout, I convinced Yamaha to let me take an R6 as a long-term/project bike, and it was my daily rider for 4-5 months (well, swapping between that and a Kawasaki ZX-14, my other project bike). I tried re-gearing it with the sprockets, but the bottom line is that the internal ratios are designed for the track - the super-tall first gear is great in that it allows you to use first for slower corners at the track, but it absolutely sucks on the street - just pulling away from a stop requires massive revs and tons of clutch slippage.
When I lowered the gearing it helped with the tall first and second, but the upper gears became somewhat too short.
Also, your experience may be different than mine, but everyone I put on the back of the R6 absolutely hated it. My 100lb then-girlfriend described it as a "leather-covered piece of concrete".
When Honda released their new 600RR for '07 (when the R6 won our shootout, it was competing against the 05-06 600RR, which took second), I really felt it was an absolutely fantastic bike. Rode it at the press launch at Barber in Alabama (http://www.motorcycledaily.com/07december06_cbrpt2.htm
), and then my best friend bought one (on my advice), and I did a few track days with him where we swapped bikes around. Although the 600RR may give up a slight edge to the R6 in the handling department, it more than makes up for it (IMO) with its easy to ride nature, broad spread of power (tons more midrange, with similar top-end), and comfortable riding position. The 600RR is also extremely light, which is great in quick left-right transitions and in low-speed maneuvers.
To be completely honest, having ridden basically every bike on the market, there's only two sportbikes I'd consider buying right now - the 600RR or a Yamaha R1 (fantastic bike, but probably a little too much for your skill level, no offense).
Things may change with the introduction of the '08 R6 - Yamaha has applied the variable intake length from the R1 to boost midrange power, and the already stunning chassis has been further refined. I haven't ridden it yet (missed the intro), but it may be the new king of the class. However, when the new R6 hits the showrooms, it's going to be in high demand, while the slightly overshadowed 600RR will be sitting their waiting for someone to negotiate a killer deal. The demand for the incrementally improved new bikes always means that last year's model can be had cheap.
Trust me, buy the CBR. Just don't get the new flat-black 'Graffiti' paint scheme - because that will be my new ride in a month or two.
And yes, that is me in all the 600RR pictures, and most of the 600 shootout shots (the grey and black leathers, or the blue jacket = me, the red and black leathers = my dad). All in the family - my younger brother took that incredible R6 wheelie shot, and the background blur is NOT photoshop.
And yes I do look like I'm riding like shit in the pics from the 600RR intro - it's hard to learn a new track when you're a Cali boy and it's 36 degrees outside (+wind chill!)...
The infamous 16krpm, 90mph first gear balance point: