Joe's pretty much summed it up - the only thing I'd add is that carbon forks also take a fair bit of road vibration out of the ride - they're a good upgrade.
Re: the shifters, do try Sora type to make sure you can get on with them - the groupsets that allow gear changes from the drops are 9 and 10 speed (currently) so an upgrade there means changing the entire drivetrain of your bike (as Sora is 8 speed). Not cheap. Also, the shifters gears etc on the SCR3 are slightly better (Sora group, the SCR4 has 2200 equipment, a level below)
I disagree with Joe on the tyres that come as standard - I thought they were bloody awful - lots of punctures, and the rear began to separate from its wire bead after about 300 or so miles. Personally, I'd budget £30-40 to replace them with something better.
I agree about the saddle - too wide and cushy for my taste, but it's certainly serviceable in the short term. I eventually replaced mine with a Fiz:ik Arione, which I'm much happier with.