Zap's review of the Chenming ATX-301/Antec LANboy/Aspire X-Sonic
Actually just the original Chenming version, but all have the same basic chassis differing only in side panel, front face and color. Unless you want the absolute lightest case possible for a normal ATX sized board (never weighed them, but IMO is lighter than the Skyhawk cases by a bit - no longer have my Chenming but I do have a new/unused Skyhawk in the garage), I wouldn't recommend it at this time because the airflow, while awesome for an 80mm fan, is still an 80mm fan, plus the case is very flimsy - mine became permanently and slightly bowed in at the bottom just from the weight of my complete system (was my "main" rig at one time).
My wholehearted recommendation for your purposes is the Antec Super LAN Boy, especially if you can get it for cheap after rebate (typically CompUSA does that from time to time). It is very lightweight without being flimsy as long as you don't cut up the case from modding and keep the side panels bolted on. The finish doesn't look too terrible if scratched up. It is very compact. It comes with carrying straps which you'd have to pay $10-20 extra for, and these are better than some third party straps that I've seen (and still own). The 120mm fan size is great for ventilation - stock fans are okay, nothing special but not terrible - they do their job and are reasonably quiet for reasonable airflow.
Couple more thoughts on things. Carrying straps will eventually cause wear marks on your case, but the "natural" finish on the SLB case doesn't show wear/tear as much. In an extreme instance you can always refinish the case a bit. The door over the drive bays is removeable. I haven't done that because of my mismatching optical drive and the fact that I'm worried that I'll break the door itself, but the case looks fine without it unlike other cases that do not look right if the door is missing. The biggest beef I had with the way the case looks is the "waffle grill" over the front fan. The easy solution is to remove the grill (really easy) and just install a fingerguard with the stock screws that attach the fan. Indeed
my own SLB case has a bling bling finger guard on it from the biggest LAN party I attended - nice touch IMO.
The case is only a small part of the overall weight of the computer so you'll want to put some thought into the rest of it
if you are serious about weight reduction. First, unless you need terabytes of drive space, use only a single hard drive. Get one 500GB drive instead of a couple of 250GB drives. Drives add weight. One optical drive only. No floppy drive. No all-copper cooler on CPU or GPU. If transporting often, consider NOT using a "tower" style heatpipe heatsink - stock HSF is perfectly fine even if overclocking he CPU will still run a lot cooler than video card. One last thing is the power supply. Good PSUs are typically heavy, but the Fortron "Green" PSUs who's part numbers end in "GLN" are really lightweight for their quality because they are so efficient that they don't need to have huge heatsinks in them. Also, you only need "enough" power (as long as good quality) for your system - no need for a monster 600W unit.