I use hot air (Hakko 800 series) and have placed SMT stuff on both sides. One wasn't really a challenge as the components that required more heat weren't back to back on the board.
In my typical double sided SMT situation, I'll have a few small caps and resistors on the bottom of the board, with most of the components on the top. The small components don't fall off; I guess they never get hot enough to melt, or they are held by surface tension of the solder.
My boards are small, with few components on the bottom. YMMV.
-j