I did not realise; after you have unlocked the last customer (and got the first hard badge), there is no need to bother serving the gold customers properly. They never stop being gold, even if you give them raw uncut unembellished pizzas. :D
Wow, I managed to finish the game with 26 lives.
Here's a tip for people who are finding it hard: Make small movements where possible, because it's easier to change direction that way AND you aim better. Manoeuvre between enemy ordnance, not around them. Try to stay off the floor, it hampers your movement. Every time you miss a heart it's equivalent to losing a life. You need to get almost all of them! And finally, every time you play you're getting a little better. Keep at it!
I happened to be playing while compiling stuff and the game started running SLOWER the higher the mulitiplier gets. As well as this, I found that the level Keep Falling (Like the Rain) is IMPOSSIBLE to lose after multiplier x6.2 - it just goes through the floor. It's still running while I type this.
Erm, got to wave 29 and my ship instantly got pushed into the far top right corner and I was unable to move it; just watch my health go all the way down. Is that normal for that boss, or did the game just screw me over?
 "N3wton")
 "The Necronomicon")
 "Hover Bot Arena"){kind=icon}
 "Ragdoll Avalanche 2")
 "Vector Runner")
 "Papa's Pizzeria"){kind=icon}
 "Battalion: Nemesis"){kind=icon}
 "3D Logic")
 "The Visitor"){kind=icon}
 "Ragdoll Invaders")
 "Grid16")
 "Aliens Must Die : The Jupiter Wars")
 "Chronotron")