not to often stolen; as broken into, if it looks likes it got something that someone would want, also depends on region too i guess but not to often. if you google search top cars stolen you will see it is mostly cheap imports here is a list i found real quick
1. Toyota Camry
2. Honda Accord
3. Honda Civic
4. Oldsmobile Cutlass
5. Jeep Cherokee/Grand Cherokee
6. Chevrolet Full-Size C/K pickup
7. Toyota Corolla
8. Ford Taurus
9. Chevrolet Caprice
10. Ford F150 pickup
as for what you can do be like me if you can take it with you do it, i always take ipod, faceplate, and then cover anything else, i have a self and cover for my sub and amp that are actually going soon, to make room for cage/toolbox/jack/whatever else i decide will fit in the back, also as far as theft do a simple kill switch for the inertia switch or something else that kills a system that only you know about