That's very topical, Simon. There's another discussion about whether there's any benefit in taking more than 30 subs.
The answer is that you'll collect the same number of photons with 600 x 6 seconds or 6 x 600 seconds but you have to consider the effect of read noise. If you have a very low read noise camera and 6 second subs are sky limited (i.e. the effect of read noise is negligible) then you'll get the same final SNR either way. If you have higher read noise and the short subs are read noise limited, then you'll get lower SNR from the many short subs.
One of the best things you can do when imaging is figure out what exposure time is needed to get sky limited. There's a thread by Shiraz which describes a clever method for doing this:
http://www.iceinspace.com.au/forum/s...d.php?t=117010
The attached graph shows the effect of read noise on overall SNR.
Cheers,
Rick.