I put in a claim late last November for a can of Tiger Beer that went missing from one of my bags when I was in transit at LAX and my bags underwent inspection before my domestic flights.
When it was the only thing missing in my bag when I got home I was pretty miffed (it was just a little gift for my dad).
So you gather your document: boarding passes, copies of your check-in bag receicpt, the TSA card/sticker, itinerary, tickets and a receipt for the item. The TSA has a list online (don't bother calling, you just get a message saying go to the website). I didn' t have a receipt (free beer!) so I just went online and found a price of $3.95 from Yahoo Shopping and gave the TSA that.
I mailed the documents at the beginning of Dec and received a check for $3.95 over memorial day weekend (6 months).
Whether carelessness/theft it should be reported even for these little things (because they may move up to bigger things later). And helping to get rid of sloppy/dishonest screeners helps the image of those guys that are just trying to do their job right. I wasn't after the $3.95, naturally, but if they had a problem employee, I was hoping my report would help them get rid of him/her.
IMHO