I'm currently also thinking up a few "zhng" to my robots:
1) Roomba Aerovac bin power up - Maybe I grab hold of a High Capacity Sweeper bin (the one with nothing inside), install a high power fan (those people use to cool their Monster graphic card), power separately or directly from Roomba battery.
This is to emulate what Neato is using for their vacuum design. Then the Roomba can sound like Jet plane taking off also.
2) Neato bristle brush - Robotreviews already discussed about this & its feasibility. The argument is that bristles will leak air while rubber flaps don't. Leaked air would mean drop in suction power. Hence, the original 500 series red bristle brush was alternating bristles & flaps.
I also find Neato beater brush is not optimally designed, it's straight cut instead of Roomba beater brush which is slant cut. Slant cut would mean that part of the beater brush is always touching ground, while straight cut would mean beater brush alternates b/w touch, no-touch, touch, so on... This translate to vibration, hence the loud tank-like rumbling noise:
http://www.youtube.com/watch?v=H9wZMzYW4J8
Perhaps Neato did it on purpose, so that the vibration can whack the h*ll out of carpet & cause dust clouds which will be vacuumed. That's the price to pay for having no bristles to comb carpet.
3) Neato sidebrush - Perhaps the easiest & most crucial mod.
Believe me, having a 4.5 cm untouched wall edge is unacceptable:
http://forums.hardwarezone.com.sg/showpost.php?p=57921142&postcount=8361
I can either install a motorised sidebrush, or better yet... a sidebrush that borrows Neato's forward movement when wall-following.
So it's like a spring rubber roller (like those inside VCR) that presses the wall, and as Neato moves forward, the roller rotates & transfer thru gears to a sidebrush which will rotate anti-clockwise.