It's not that bad (oh no, I'm quoting Imperials), even if you're on foot. Of course, it depends on what route you choose. If you decide to travel via Windhelm, it's obviously going to take longer than if you went through Falkreath Hold or followed the "Riften" signposts on the road from Whiterun.
In any case, the sights and random encounters will make sure your trip won't be boring.
I've entirely stopped using fast-travel, with few exceptions. "Season Unending" would be a pain not to fast-travel, as would a "Rescue Mission" where an NPC has been kidnapped to the opposite side of the province... or to Solstheim.
"Slow-traveling" is definitely much more enjoyable -- except from Riverwood to Solitude via Rorikstead (during "Diplomatic Immunity") if Alduin's working his magic. There are three mounds along that road, IIRC. -.-