Actually the time sink from 10 to 40'ish is probably the worse, but once in Tanaris (or where ever) things start to smooth out for a bit until 55 and then try and run some dungeons if you can, if not I've heard going to hellfire penn and killing the little demons by thrallmar/honorhold is a great amount of xp and you can catch 58, like 3hrs.
Then outlands is a breeze and as "most" of Northrend is bug free you can level there pretty fast and doesn't really slow down until 77/78, but just focus on your quest and you'll be 80 in a few hours.
/shrug
I didn't mind so much, the real grind is endgame. Getting into heroics isn't that bad, especially if you do your Icecrown quest and run your normal HoL, HoS, UP, and CoS. The problem i've been having is finding a stable community, as a lot of guilds seem to not hang around for to long and eventually fall apart, this in no way is Warmane's fault, but for some reason people just don't know what community is and what it means to be their own guild.
I've been through 5 guilds since i got to endgame and around 10 since level 14 when I joined my first guild and almost all of them fell apart, besides one that just never talked to one another and then another one that was pretty toxic, so i bailed out of that one.
Summary, leveling isn't that bad, endgame and finding a good community is rough.