WoW blogs have recently all been abuzz with news of the upcoming class changes in patch 3.1, but somehow I haven't seen any mention of the planned changes to mana regeneration. The gist of it is that they think healers have too much mana regeneration - DPS casters are basically always casting, meaning they only benefit from MP5, while healers often get high mana regeneration by staying outside the 5-second-rule and getting mana back from Spirit. The issue is further exacerbated by various clearcasting-style procs that allow you to cast a spell without using mana, thus still being considered "not casting". To fix it, they will probably make Spirit-based regeneration lower (while making talents like Meditation stronger to give roughly the same MP5).
Now, I don't know what's going on in heroics or raids, but in all the instances I've healed recently I think I only ran out of mana twice, while still having a potion, Inner Focus, Hymn of Hope and the racial Arcane Torrent. In fact, I usually finish most trash fights with full mana. So I can see where Blizz is coming from, and why they want to "fix" it.
However, I'm not at all sure that reducing non-casting regeneration is the solution. First, it would basically demote Spirit back to its old status of "that other stat no one cares about, but seems to be on a lot of caster items". No wonder they're making Divine Spirit a baseline spell for all priests - who'd pay a talent point for such a useless buff? Also, I don't know about other healers, but for me dancing with the 5-second-rule is one of the most enjoyable aspects of healing as a priest.
But, just criticizing without offering a solution of my own won't help, so let's see if I can't think of some other ways to solve the issue. Reading Blizzard's post, they mention 2 specific "problematic" areas: Clearcasting procs and HoTs.
Clearcasting procs let you heal while still benefitting from full mana regeneration, since they don't cost any mana. Blizzard is currently thinking about changing it so that they will return mana when proccing instead of giving clearcasting which, to be honest, makes it much more boring. Instead, they could change clearcasting to cost 1 mana. For all intents and purposes, it's a free cast, but it puts you in a "casting" state gimping your mana regen.
HoTs, especially the long ones, let the healer put up a relatively long heal and sit back and wait for the mana to come flowing in. Now, the only healers who can realistically stack enough HoTs for this sort of behavior are druids. No reason to punish all the priests, paladins and shamans for something that is not only specific to druids - it's the basic concept of druid healing. But let's play along and assume that HoTs are problematic. There's a very easy solution for this - give HoTs shorter durations, let's say, oh I donno, 5 seconds. That way in order to keep someone healed you don't get the chance to leave "casting" state.
Still not good enough? Change it to the 7-second-rule. That way, they still keep Spirit an important stat, while still being a little weaker. It will also require more skill to dance, although whether that's what Blizzard want or not, I don't know. Of course, they say that they don't want "sloppy players" but they also don't want to make things too difficult so they don't scare healers away...
So where does that leave us? Same place we were before this post - Blizzard isn't really going to listen to me on important things like mana regeneration.