Just got my new machine and grinder and had it for a few weeks now, its been so much fun entering into a new world of discovery.
I have been playing around with a few different roasts and trying to extract the flavours of the coffee. I noticed when I went from a medium roast to a french dark roast that if I kept the grind the same the coffee tasted really bitter and too strong. So after a bit of playing with the dark roast I found that grinding much coarser, over dosing and tamping heavily to stop any gushing produced really great and tasty results!
Likewise I have noticed that with my favorite medium roast if I grind finer and pull back on the dose I get super smooth flavour with lots of chocolate and caramel tones.
It seems getting the best out of a certain roast and blend depends heavily on grind/dose and tamp?
@Andrew, there are some amazing articles over at HB on this topic under the title of.. "mano" something. Anyway its all about how you can change your dose/shot time to push the flavors in different directions, your example with the dose is echoed in that it says lower dose leans to caramels while higher is acids and bitters (not bad ones!).
Another one is that making the grind coarser to get your 1.5-2oz shot out in less time, maybe 20-25 seconds bumps up the brightness. I think you can increase the strength of the bitters going in the other direction but I don't often do it =)
I'm very much in a learning phase, but I do find that I enjoy the taste of some beans (partic. Centrals) with a lower dose / finer grind (16g in my double basket, as opposed to a normal 18-19g.....). This is sort of consistent with David8s remarks above, coz I tend to roast those beans a bit lighter.