Input capture on pin 8 is the most efficient and accurate way of measuring pulse widths at the same time your sketch is doing something else. There is only one Input Capture pin so you would need to measure the composite signal where each channel pulses in sequence followed by a relatively long (at least 4 millisecond) sync gap to indicate the start of the next sequence of channel pulses.
A code fragment for Input Capture was posted in this thread http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1201890734/12 It would need enhancing to recognize the sync delay and then store the widths of the channel pulses.
Assuming you are driving this from a radio control receiver then you could 'or' the channels together to get a composite signal to feed into the Arduino input capture pin.
Or you could use a receiver that has the composite signal somewhere on the PCB. I have been poking around with the Hitec [u]HF-05s receiver[/u] recently and if you can do the precision soldering to the tiny surface mount pin, this should work. These receivers are small, reliable and inexpensive; versions seem to be available in every country where RC equipment is sold.
This receiver uses a Pic [u]16F676[/u] microcontroller to decode the pulses from the radio circuit and drive the servo pins.
One of the Pic's pins has the composite signal at digital levels suitable for driving an Arduino if you can solder a tiny wire to the correct place on the board to get at it.
Pin 11 (RA3) has the composite pulse train at digital levels. The radio circuit powers the Pic through a 5v to 3.3 volt regulator so the output pulses are 0v low and around 3v high.
FYI, Pin 13 (RA0) is the composite input signal from the radio circuit.
I don't have any more code than I have already posted so unless someone else has done the work and can publish it here, you would be pioneering this. I would be glad to provide advice and I am sure there are others with similar applications would benefit if you published your results.