Matt, splitting is something we wanted to have for a long time, but sadly splitting just in two is not enough.
Users love cramming several things into one entry.
Here is just one example: http://illustrator.uservoice.com/forums/333657/suggestions/39813334

Initially I though that I can split a list like this into two, then grab the second and split it further — but no, the secondary idea can’t be split any more :(

Can it be upgraded further?

The ability to merga Ideas is fantastic and saves a lot of time. It would be helpful if we could also separate Ideas and maintain the existing votes and comments.
For example, I have an Idea where the user lists multiple third-party products. For us to properly prioritize we need each third-party product to have separate Ideas. The only way I can manage this now is to create a brand new Idea for each one then add the contributors after.

I liked this capability, but it would also be nice to include the comments, feedback, and votes to both ideas when the idea is split as well. Sending a notification of the split and the vote would allow them to "unvote" but reduce action required by the user if they liked both ideas.

Very common for the user to post multiple ideas in one go. Comments here are on spot.

I'd like this capability. Users often post multiple ideas in one go. I know I can create new ideas and copy and paste, but I then lose track of the author. Ideas have more credibility if they are raised by users and not the admin.

We should be able to split the idea into two feature components.
We should be able to choose whether to copy the supporters into both, leave them in the original, or move them to the new one.
In the end, we need to make a decision on how to interpret and implement.
Also, allowing the option of splitting an idea/suggestion into engineering implementable features help provide greater transparency and communication on progress.

We also have this issue, sometimes users submit an idea like "add something and allow something", which translates to two very different features: one that's an easy fix, and another that will take months to implement (if ever).

With regards to votes, I think whoever voted on the compound idea voted on both. After the split, both new ideas should keep all the votes (preferably without affecting the number of votes these users "have left" i.e. can use).

I find this a problem for the forum I manage. I would suggest that at the point we split the idea, the voters are sent a notification of the split and can re-assign their votes. That would solve the voting concern.

In regards to changing the idea, I don't feel this is necessarily a problem, since we can already 'edit ideas'. What we need, is to split an idea which may refer to multiple features, which, according to our roadmaps may have differing priorities. We don't want to lose anything in the suggestions/ideas users are putting forward, but in the same vane, we don't want to have an idea status changed to 'completed' when only half the idea has been delivered.

Create a new idea manually prevents the user who submitted the two ideas from receiving updates to both ideas, but will only get it from the first one.

My initial instinct is that this is more trouble than it's worth - both for us to build and for your users. Most of the time you can simply ask them to post a second idea, or you could post it yourself and direct people to it. But the votes concern coupled with the fact that you're literally changing the idea they're posting seems like it would make this troublesome for your users. Interested to see more opinions though.

Thanks Coleman, agree.
Could you please vote this up, its currently still got 1 supporter (myself)?

You could also allow people to vote on splitting ideas. It's often pretty obvious how ideas need to be split up, so I think users could be trusted to spot it most of the time.