I have been using Ubuntu for a few years, but aside from a little bit of playing around it's pretty much the only Linux based OS I have used. To my understanding, Xubuntu, Kubuntu, and Lubuntu are just Ubuntu with different desktop environments and default applications. The Lubuntu page on the Ubuntu wiki specifically says that, and that it shares Ubuntu's repositories.
I've just now learnt that Kubuntu 13.04 doesn't provide auto installer for dual boot system. Ubuntu provides. Lubuntu provides, Xubuntu provides. Kubuntu force you to install manually. Do partition, install and set GRUB, etc. So painful surprise. Only two alternatives, either it takes 100% of disk or do it yourself.
For this new Long-Term Support release, major changes have been implemented, not only in Ubuntu, but in its derivatives as well. Trusty will be supported for five years for Ubuntu, Kubuntu and Ubuntu Kylin, while the other flavors using a different desktop environment will be supported as well, if only for three years.
One of the best things about Linux is that there is so much to choose from! Ubuntu Linux, for example, has official and unofficial variants with different desktops. There's Kubuntu, Lubuntu, Edubuntu, Fluxbuntu, and my personal favorite, Xubuntu. They're all Ubuntu "under the hood" so to speak, but very different from one another at the same time.
Lubuntu 14.04 LTS (Trusty Tahr) has been officially released and joins its brethren from the Ubuntu family – Kubuntu, Xubuntu, and Ubuntu GNOME. The Lubuntu developers don't usually make big changes from one version to another, and this is true for the latest build of the Linux distribution.
Lubuntu 14.04 LTS Beta 2 (Trusty Tahr) has been officially released and it has joined its brethren from the Ubuntu family, Kubuntu, Xubuntu, and Ubuntu GNOME. The Lubuntu developers have been rather conservative and they haven't pushed huge changes from one version to another. In fact, Lubuntu is the distribution that usually changes the least during the development cycle.