Man, I see it all the time in my line of work. Tired ass, worn out dudes with badly fitted and heavy ass surplus packs. Don't get me wrong, the mil makes their shit durable and heavy for a reason - so the gear will last thru years of abuse generated by 18-25 year old dudes. The only problem is that many of us aren't 18-25 anymore.
If you have surplus gear and it works for you, go for it. If you don't but currently have a job, find a deal for something lighter and better.
Like others have said, there is some stuff that'll work fine for a night or two out. A lot of the newer mil stuff is basically 10-15 year old civvie technology - and not easily sourced for dirt cheap. The bivy and jungle bag from the sleep system, the newer thermarests and the USMC ILBE come to mind.