I've used Joana's extensively for several characters. My opinion is that if you are in a hurry and plan on quickly leveling, use it. There are some caveats though....

1) It sucks the life out of you. Questing is no longer fun, it is a horrid grind. It becomes WORK. For some reason this is much more depressing than using a mod like Quest Helper or Liteheaded/TomTom.

2) If you follow the guide the way Joana wants you to, you won't be doing anything else, no professions or anything (other than first aid), so prepare to grind that later.

3) This is not a multi-boxer friendly guide. Quests that are 'Group' quests are often skipped by Joana, while a boxer would find these quests quick and easy. Gathering quests that Joana takes the time to do, would simply kill a multi-boxer.

So if you're leveling one character, want to do it fast and don't mind being a mindless zombie for a few days, go for it. That's how I leveled my hunter to 70 super fast. Otherwise, don't. For some reason, the mood is lighter when you're picking your own path, and honestly with all the quest mods out there, you can be just as effiecient while being the master of your own destiny and determining what quests are good for you and which ones to skip.

edit: Additional note - I felt compelled to say that I attempted to follow Joana's WOTLK guide while dual-boxing my priest and hunter. By the time I hit 75 I was ready to /wrist /delete /unsub. If you've got even 2 characters going at once, don't do it that way.