No. Never. Buying leveling guides is a waste of money. Any type of information covered in Zygor is more or less found all over the internet. Leveling is so fast and streamlined now there shouldn't be a reason to use a guide. Go to the zone recommended for your level and do about 20 quests and you're already on to the next zone, outlands, northrend, and cataclysm content is so fast now you can do all 5 or 10 levels of the expansion in one or two zones.

Professions skills are split between expansions now, you'll have a separate skill bar for each expansion. There are still 950 profession levels in total, just that there is no one single progress bar with 1 to 950 for it anymore. Instead, there are 8 separate progress bars. (The only exception is Archaeology, because it will still have a 1-950 progress bar)
Hi, cool addon, but I have one problem with it, the objective quest location is now changed into the top of screen and cannot be moved, because I also use "MoveAnything" addon and I use that addon to locate my quest objectives, now I think both addons are causing a problem where I can't move the objective with neither of addons, for example even if I unlock and try to move using Dugi, it won't move, it is stuck in the top of screen just above my minimap.

Picking up herbalism and mining is the best professions to have while leveling. Not only will you earn gold as you level, but you will also get extra XP. At level 20 you will get over 500 XP for picking up a ore or a herb while killing a mob only gives a little over 100 XP. Don’t go out of your way to pick herbs if you are trying to level quickly, but pick the ones that are on your way. Leveling from 110 to 120 can be done pretty quickly just by doing this. There are a few items that will help you if you decide to use professions while leveling:
DoTs: Assuming that the mob is going to live for certain periods of time, it is worth it to place DoTs up. If the mob lives for at least five seconds, cast Pain. If it lives at least seven seconds, cast VT. The ideal time to cast DoTs is when it would be replacing Flay, but you can substitute Blast if the mob will live longer. Make sure to cast Bolt on cd though!