i like the red pcb & the two LEDs (yay!) - sometimes people dont include them but i think they're essential. the high voltage 3.3v regulator is a good deal too. also digging the .1uF on Aref.
the 5v/3.3v shield thing is not a -huge- deal: avr's are (im like 99% sure) 5v compliant so, at worst, it should still work. (if using a r divider, then 1.8V is still higher than most CMOS Vih)
ironically, if you actually solder in female headers to put a shield on it, it will be exactly the same height as a diecimila 
theres no 1k series resistor on RX0, which means if you've got a GPS (or xbee, or xport, etc) connected to rx/tx - many tutorials/examples do this - and the serial link installed (for debugging/uploading) its going to perform very strangely. if its not included, it should be noted
the switch would be 108914981273 times awesomer if it was RA and on the board edge so you could turn it on/off when a shield is on. no big deal tho. (i am rooting for a right angle 3pole switch in the next arduino rev.)
is the 3.3v on the serial connection an input (to VCCIO) or an output (from the internal miniregulator in the 'RL). if its the latter, thats kinda sketchy. :-/
the fuse seems a bit odd - the diecimila fuse is there to protect the computer's internal usb hub. a reasonable 3.3v regulator (you dont have the part number anywhere so i cant check it) should have short circuit protection. and avr's are current limited on the pin. what would be -really- useful is a power diode, such as a Schottky or 1n400x so when they plug in a 9V backwards it doesnt kill the regulator (good ones have pol protection but most cheap ones dont) and then heaven forbid, if it fails short pass the -9V down to the avr and everything connected to it 
good news is that you can get 1A diodes in supersmall packages so ya can reuse the pads!
and one last thing:
i dont really get the 8mhz/'lilypad' thing. i use internal oscillators all the time for cheapie kits, but i'd never do it for a project where customers are expecting to use a serial library where they cant tweak the TCCR values (and where the bootloader is pre-burned with a set value that is not calibrated). i've found that the int oscillator does vary a bit over large runs/temp/voltage. why not include (at least) a ceramic oscillator? you can get a skinny one for $0.20, a full-on crystal setup is maybe $0.35 or $0.40
ok i think im done now