I know what you mean - I have a similar story.

I was a dedicated horde character - 3 seventies and I was having fun.

Then news of Wrath came out and people started to wander away. People I had played with for months disappeared without a word, and my guild died a slow and painful death.

I couldn't face pugs and couldn't face solo levelling yet another character and so investigated multiboxing. I used it to boost a couple of characters - one to 40 one to 53 then abandoned them.

Then RAF came along and I decided to get a team levelled. I rolled the 4 shaman and 1 pally team and got them up to 60/61. Fantastic.

However round about this time I re-established contact with some friends I'd met in the very first guild I was in. These people are the most friendly and generous people I have ever had the privilege to meet online. They had moved to the alliance side and had multi 70's to play with.

I had tried levelling a character but found it dull and didn't want to ask them to boost me.

So I decided to take the opportunity RAF afforded and level a second team to 60. This time I rolled 3 mages, later dropped one of the mages and ran a 2 mage 1 druid team to 60 and gifted a palladin.

By this time the druid had emerged as my favourite character of all. Patch 3 arrived and at this point I got focused on levelling to 70 to do heroics and instances with my friends. My multiboxing stopped.

I'm having a blast with the guild now though. Running instances with a group of friends just beats multiboxing for me.

My multibox team aren't going to laugh or pull my leg after I rashly dropped a star fire on Big bad wolf in Karazhan and wondered why there were a ton of mobs run in half way through that wiped us out (I'd pulled the audience - not the sort of audience participation you want).

Wrath is imminent and I will focus on getting my druid to 80 to keep that fun going.

My RAF is over, and the only regret is not having levelled the pally and shaman team on the alliance side.

I am not giving up multiboxing, it's just taking a back seat for now.

So to the original poster I would say - so long as you are having fun it doesn't matter if you are playing 1 character or 5.

I'm sure that you will be back to multiboxing at some point.