Maiandra and I have played a few of our characters and came to the following:
Cleric (level 24)
Grouping: Habba-habba! No more 'get back on your butt' attitude

I can finally use my big whocketystick the way I want to. And if people think I'm gonna refrain from using my virtually no-mana yaulp, they can talk to the stick >

Solo: Basically, if a mob turns out slightly harder than suspected, I'll either die or cause a train. No rooting it to back off and bind wound, no rooting it to med for a heal, just rooting it to get a head start when running to the guards/zone. The lower downtime medding is nice, but I'm not sure it doesn't balance out with the time I spend running/paying off an xp debt. Biggest advantage: faster medding decreases the chance of something popping on top of me without mana.
Enchanter (level 24)
Grouping: Mwuhahahaha! Everybody will now need us (and bards) even more than before. If at the end of a pull there is an add that the group can't take (low hp/mana), *we* can charm the mob, making it not count as an npc, allowing the group to med. And it is awesome to be able to use my entire array of spells, stuns, buffs, nukes, without having to think of it as not mana efficient. It takes only half a minute to get all that mana back before the next pull, so let's blow it!
Solo: A bit overpowered when I did because of the mez. Once that's fixed I guess it'll be the same for me as for the cleric, except that I could still try to charm and med up instead of having to run immediately.
Necromancer (level 30)
Grouping: Well I never much cared for grouping. I need stuff that stays alive for a bit so I can effectively leech from it, and in a group everything is either mezzed or dead before my spell has been worth the mana it cost. For the same reason, dotting while grouped is pointless. However, with downtime for medding being both short and expected, I'll not feel bad about using my debuffs on every single mob we see, and maybe even my nukes. Just hope the debuffs stack with those of other classes, I've never bothered to try that out.
Solo: Oh, no, no. Please don't do this to us :sadf: My downtime has effectively doubled, and my hitpoint-to-mana spells are therefore worthless, because they just get me lower on hitpoints. The mana gained during fights isn't worth it compared to just sitting afterwards without it. In fact, I discovered that I'm most efficient (kills/time) by sending in the pet and occasionally healing it while not wasting mana on anything else... I'm my pet's cleric bot! :lol:
Paladin/Shadowknight (level 17)
Grouping & Solo: We never got to med during fights anyway, so as far as we're concerned: Yay!
Druid (level 42)
Grouping: Haven't had a chance yet. I'm a little concerned that during longer fights the tank will now expect me to keep every bit of mana for healing, while I like to think of myself as more of a utility caster. And if I'm expected to whack, could my Starfall staff get a better damage/delay than 10/45? Otherwise, I'm still better off staying our of reach.
Solo: My armor class doesn't allow for tanking, so running oom now means I have to give up. At least I have the advantage of always being SoWed, so I don't have to rely on a root to outrun the mob.
Rogue (any level, really)
I don't see why everybody complains about being less able to solo. I don't get to bandage, you don't get to med. Sounds fair to me.
Conclusion:
For most group layouts, this seems rather nice. For pure caster classes it might be preferable to have the old system while soloing. Wizards, I'm sure, won't agree.