I ran Death in Freeport Tuesday. They didn't quite finish, they've got two more combat encounters to go, otherwise they breezed through the first three combats (well, they'd hardly agree with 'breezed' we had multiple people at 0 hit points at various times!), and the assorted roleplaying / information gathering / traipsing around town in-between. I spent 2 hours one night re-writing each of the combat encounters, and the NPC, because I didn't care for their stats, class choices or feat choices (or equipment). 8 1st Fighters, 1 1st Archivist, 4 1st Fighters, 1 1st Battle Sorcerer, 1 2nd Urban Ranger (duel-wielding MW Throwing Axes), 8 1st Barbarian Serpent Men, 2 1st Clerics, 8 Skeletons (enhanced by desecrate), 1 3rd Cleric / 1st Sorcerer. Easy enough. I also reworked the Serpent Folk to be LA +0, since LA races, like NPC classes, bug me and ahm agin' em. I also did some weird and useless stuff, like give the Sorcerer a few ranks in Craft (scrimshaw) and change his 'loot' to stuff he'd crafted himself out of whale ivory and gave him a Flying Lizard familiar that scoped out the party before the ambush (they blew the Spot check to notice that). I like giving the 'name' NPCs little hooks like that.
I'll be running the end of Death in Freeport and either an intermediary story or the beginning of Terror in Freeport next Tuesday, and it took me 3.5 hours to convert all of the NPCs and Monsters from that adventure. I got slowed down because I changed 10 cultists into Cleric 1 / Rogue 1 and the skills took awhile to type, since I don't have a standardized form (note to self, make standardized template!!!). Plus I was watching the Sarah Conner Chronicles at the time, and kept looking at the evil machine to see if Riverator was gonna take her clothes off again this ep.
I read about how incredibly time-consuming writing characters is, and I wonder how that is. One of the players last Tuesday didn't have books and *had never played 3.x* (he had played 2nd edition), so it took him, all by himself, 10 whole minutes to write up his character (one of the other players expressed annoyance, as he wanted to play on his computer while waiting, and didn't have time to get his game loaded).
I also read about how incredibly hard it is to run combats in this game, and yet the combats were all over lightning fast. Initiative, go, go, go. Next round, go, go, go. I use dice instead of figures, so I just wrote down which number took which amount of hit points. Number three takes eight. Number six takes 17 and drops, Fighter cleaves and misses. Wizard goes. Druid and psycho riding Dog from hell go. Dog gets a Trip attack, ooh, there's an added die roll, which takes an extra second or two if the die doesn't roll off of the table. End of round, mook eight fails to stabilize and is dead. Fighter goes again.
I deliberately slow it down with descriptive stuff about scimitars bouncing off of shields and axe-blows so hard they numb your arm, but it still plays fast.
GURPS and Vampire require a lot more book-flipping, in my experience. d20 is pretty darn fast. As a GM, you can generally keep all of the rules you need in your head, unless you have no actual plans for the evening and are whipping up an adventure off of the top of your head, or by doing the old 'open the MM and point at a random page, that's what your fighting' technique. (Not that there's anything wrong with that, the random dungeon generator from the 1st edition DMG was indeed a hoot at times.)
If I had to pick something in 3.X D&D that slows the game way the hell down it's people who use Summon Monster (or Summon Nature's Ally) and haven't got the beasties pre-written out in advance (adjusted for Celestial or Fiendish, Augment Summons and / or Augment Elemental). That and Evard's Black Tentacles. I just house-rule that to make it faster. Pain in the butt spell, but not really enough to warrant a new edition, IMO.