On my last raid in Ulduar 10-man I got a chance to try some solo healing. I did the arena at Thorim with ease (probably had at least 75% mana all the time:)) and later Razorscale (used one Hymn of Hope at the landing - not much to do at that time anyhow). It was exciting and fun of course but then after a day I wondered... Why are we doing instances/modes that can be solo-healed? This must be an indication that it is time to move on, or scale up the difficulty quite a bit.
On a side note, when I solo healed I seemed to keep a higher mana-pool than otherwise?