I introduced my old friend Nate, who keeps an irregular blog, to RPGs around about a year and a half ago, and he is now running a LotFP campaign set in a fantastical simulacrum of real-world Finland. It is interesting to see somebody's DMing-style develop. I was in (I think) the first session of a game he DM'd, and so I have seen him progress from a novice to a regular, running proper campaigns. (Little Nathan has all grown up.)
What is most interesting about this is that I have noticed that Nate is very strong in two areas that I see as my weaknesses - creating very memorable NPCs on the fly, and creating a more fairy-tale kind of a mood. My NPCs tend to blend together, unless I put on a funny voice or accent, being universally sarcastic, cynical, mean-spirited, and rather unhelpful. (Except if they are women, in which case they are just overtly flirtatious, even if they are 80 years old.) I'm not sure why this is the case, but it's definitely the area I need to improve on most.
And the mood of my games leans towards the gritty; I don't do the fantastical very well. Nate has a good line in the fairy-tale-esque - I'm not sure how intentional it is, but there is a heavy dose of the Brothers Grimm and a (very dark and bleak) Hans Christian Andersen in his work. I like the tone of my games, but I would also like to be able to vary it, and bring in some fairy-tale flavouring from time to time.
It's interesting, don't you think, that learning from other people's DMing style is something that is almost never remarked upon in the RPG blogosphere? It's often noted that people who blog are very good at creating content (monsters, spells, maps, etc.) but very poor at discussing more fundamental issues like how to be a good DM. I'm reminded once again of Zeb Cook's advice in the 2nd edition AD&D DMG: "Take the time and effort to become not just a good DM, but a brilliant one". That must start off with learning from others, but in general it is something we tend not to talk about.