ok, after playing around more with BEs (though now that I'm done with the new zones, I'm not bothering to play mine anymore) I think I can safely rate their usefulness in each class as follows:
1) Paladin - basically every single racial helps Paladins aside from the +10 enchanting racial, which helps if you decide to be an enchanter. Mana tap can be used to pull on mobs with mana, arcane torrent gives an interrupt (because really, 2 seconds of silence isn't much at all most of the time) and can also provide some quick mana. I think Mana Tap is bugged and doesn't give mana to the user, because Blizz's SCT ripoff shows a mana gain whenever I use mana tap, but I don't actually gain mana. It's probably more likely that blizz's SCT ripoff is reporting it incorrectly though, cause it's +71 mana at level 21, and it's on a 30 second cooldown... even with over 1k mana that's a good instant boost to mana and you'd gain more than an equivalent level mana pot using it 4 times vs 1 mana pot (same cooldown in total time). Still, if you go enchanting every single racial is golden for a paladin, and if you don't, then 3/4 of them are awesome.
2) Rogue - Basically the same as Paladins, just that arcane torrent isn't as useful due to all their interrupts.
3) Priest - Mana tap's buff lasts 10 minutes and it has a 30 yard casting range, so in a group you could easily build up 3 charges of it and then use arcane torrent when you need some quick mana. That's probably not so useful at the high end with all of the MP/5 gear and divine meditation, but still. Plus arcane torrent gives non-shadow BEs a silence (and shadow ones get a second silence), even if it's only 2 seconds, and the mana loss on your target from mana tap can help in pve or pvp.
4) Mages - Similar to priest, but only ranked lower because they get counterspell so they have an interrupt by default, and mana gems so the mana returned isn't quite as necessary. Still, they actually seriously benefit from the mana gained.
5) Hunters - Mana tap is sort of ok, but really they won't need it much. Arcane torrent is kind of redundant for a class that needs to be at range, however it's not bad in duels or pvp, and even with no target active you can use arcane torrent to regen mana. But compare it to going 41 marksman, and quite frankly, you're better off being any other hunter race.
6) Warlock - Compared to orcs and undead, BE warlocks just flat out suck. They're pretty, but mana tap/arcane torrent is ONLY useful for a silence, and warlocks tear the shit out of other casters already so that's kind of pointless. The mana gain is good (since free mana is free mana), but you get lifetap at like level 6, and drain mana at 26. So it's not nearly as important for a lock as it is any other BE mana class.
Now, I'm just rating them by racials, but seriously, BE melee are awesome, BE mages/priests are good, BE pet classes are mediocre.
BTW, BE priests apparently get touch of weakness at level 10, and Consume Magic at 20. ToW is hopefully just a placeholder, Consume Magic is interesting but weird. It scales as you level and it consumes a buff to restore mana. So I guess for a BE priest, you can consume inner fire to regain mana, since it restores more mana than it costs to cast inner fire. I really hope they get a unique level 10 racial spell.
Draenei priests get some unique spell at 10 (I don't know what, but I don't think it's the Thott datamined level 10 racial) and fear ward at 20. I really wish BEs got fear ward so horde and alliance would be totally balanced in terms of pve content, but oh well.
And speaking of Draenei, I've got to say that their mount is pretty lame. Well, ok, it doesn't completely blow or anything (nothing is blander than horses, or more retarded than nightsabers), but the Elekk is like the kodo's retarded cousin. It doesn't look too bad sitting still, but it animates really dumbly. I know it's an elephant knockoff, but it looks clumsy, and not in a cute/funny way. It just looks half-assed. Then again what little I've seen of the Draenei zones seems half-assed too. Not that I personally mind; it's good that Blizzard actually concentrates on horde content for once.