I have been playing with dual booting, only because I can. But unless one is trying to find bugs or just want to see what another ROM looks like, I do not see the benefit of it, yet.
In the end, one still gets pretty much the same experience on the same device (I know I know, I am not trying to start a war on 'which ROM is best' here).
I was on ICS Resurrection 1.1 with stock kernel, then Siyah 3.x to try out dual booting. Been trying CM9, Hydrogen, Foxhound, updated kernels, ICS Resurrection 1.3, etc.
I am now back to ICS Resurrection 1.1 with latest Siyah 3.1rc2 as it gives me the best performance so far (no, not measured, just going by my own feel). Maybe I can get more battery life out of a newer ROM but from what I am getting today versus stock ROM, I am getting a heck of lot more time out of my device already so I am happy.
Dual Booting gave me an option in the past of Linux and Windows only because there was one particular application on Windows that I used and was not available in any other form on Linux at the time.
Today, applications are available on iOS, Android and I assume Windows for mobile devices (whatever that is called) - that are the same or equivalent so a dual boot might not necessarily be very beneficial for the majority of users.
Now if there were such a thing as a specific ROM that is optimised for one use only, such as camera only, GPS/Navigation only, Music player only etc. and it really improves the performance/battery life because of it, then it could be a great tool. I am not sure if this would even be possible.
Just my 2 cents