After 3 unofficial releases, Lubuntu was accepted to become a part of the Ubuntu family back at the Ubuntu Developer Summit in Budapest. It's still not 100% certain that Lubuntu will become an official Ubuntu flavor starting with version 11.10, but it's getting there, especially since you can finally download Lubuntu 11.10 daily builds starting today.
Although a beta version of Lubuntu was released a few months ago, a blog post makes it clear Lubuntu 9.10 won't be released:
When the first Lubuntu ISO came out (LXDE based Ubuntu), it was said that it's purpose is to be faster than Xubuntu:
The Lubuntu project (Ubuntu based on LXDE) just published it's first ISO. LXDE is a very lightweight and minimal desktop environment using the openbox window manager, the PcManFM file manager, and a very select list of default applications.