Digital BW, The Print

like many of you, i suspect, i store the photos i've worked on in photoshop format so i can 
retain layers, etc, and readjust them easily later. but this creates huge files. the worst 
discrepancy is for a jpeg that was taken as jpeg and not raw; the file often grows to 30MB 
or more for a 6MP image.

my intuition -- and i'll admit i haven't checked the numbers -- is that this is much more 
space than should be needed, even ignoring the effect of jpeg compression. hence my 
question: are there some tricks people use to reduce the file size? yes, i know storage is 
cheap, but using lots of unnecessary space has its costs (eg, in time spent backing up).

obviously, i don't want to lose information by reducing resolution. but i'm assuming that 
much of the growth is because photoshop is caching information that can be deleted. for 
example, if i have all my work in layers, i'm usually happy to clear the history, and 
presumably a long history takes a lot of space. are there other things like this?

i wonder whether maybe photoshop itself is not well designed in this regard? a curves 
layer, for example, shouldn't require more space to store than the amount of data entered 
when you design the curve -- a few bytes for a couple of points -- as it should be able to 
recompute the effect of the curve from its specification. it seems not to do this, however.

any thoughts?

/daniel