For invasions (developed from reading the help of all the people posting here):
I began writing down level times last Friday, when I started leveling a horde shaman from 1 to 100.
1 - 100 took 16 hours and 7 minutes. I hit 80 at the 10h 20m mark
Yesterday, I started leveling an Alliance Hunter.
I am at 80 and my time is 8h 20m. I hit 60 at the 4h mark.
So, for the shaman, I wanted some boxes to open at 100. I traveled around much more; at about 60 I would do the first 2 invasions in the set of 3, then sit in the last one, doing phase 1 to 3, then relogging. I did the last invasion until the zones rotated. Last week also had the invasions moving around, so there was a chance every 2 hours that it forced you to move. When I hit 85, I realized that gathering boxes could have waited until Cata portals opened, and it would have cut down on travel time.
For the Hunter, I went to invasions at level 10 (same as shaman), and from 10 to 60 I did phase 1 and 2, then relogged to reset. At level 60 I went to Stormwind and got flying. Went back to Westfall and started doing phases 1, 2 and 3. In phase 3, for Westfall, you have 3 skull bosses in the south, that the horde will kill (one can be bugged out). Once all 3 of those are killed, two are due to spawn in Westfall. Run up and kill them, and immediately relog. I would also recommend getting a stack of 5 bandages from the illidari camp, north of Westfall, unless you have very good self heal. Even with the Hunter 70% self heal, on 2 min cooldown, I go through 5 bandages in about 5-6 invasions.
How I would rate XP from various invasions:
Westfall
Xroads (N Barrens)
Azshara
Tanaris
Hillsbrad
Dun Morogh (I hate this invasion)
Westfall and Xroads are close. I think Westfall would be a clear winner, if it wasn't for the bugged boss in phase 3.
I leveled my rogue from 61 to 100 in Outlaw spec doing invasions. Only once did this happen so I am not sure if it was from the RtB buffs, but I turned into a skeleton. I looked at my buffs and I had all 6 up. Is that some special side ability they get if you are lucky enough to have all the buffs going at once? Maybe it was coincidental and something else turned me into one, but I did a LOT of playing and haven't been able to replicate it, nor having all buffs at once.
Where you killing Abysal in the Westfall invasion? I know one of the treasure goblins will turn you into a skelly. Some other npcs may turn you into one in other invasions as well.