When I used LXDE, it had a long way to go before it could be considered equivalent to Xfce, and I ended up switching back. The ultra-lightweight window managers may be in fashion, but Xfce is mature and polished and easy enough for my mother to use, and I can't say that about Lubuntu.

The typical Ubuntu user probably won't miss much on Xubuntu. When they find that mrxvt doesn't let them use Ctrl-C/V to copy and paste, they'll be mystified. Ditto for Openbox's wu wei panel management.