I heartily agree with Mirax H. I've sewn sticky backed velcro to fabric, and the machine doesn't like it at all! The adhesive grabs at the needle and makes it like you're sewing really stiff/thick fabric. At best, you end up with residue on your needle which can ruin whatever you sew next, and at worst, it can wreck the machine's cogs and gears (trust me, I know from experience!)
I returned the sticky backed Velcro I had gotten at Wal-Mart and headed over to Joann's. They had sewable Velcro on sale there. My flak jacket closes nicely, I just need to put some sleeves on it and dye it.
Got my neck seal today from TK-409 and it all fits great! Need my jumpsuit soon... Can't decide if I'm going to try and tackle sewing that or not.