I'm having trouble getting rid of these white spots on my RX-7's finish and glass. I think it's dried tree sap. The stuff is raised, very hard (almost petrified), and will not come off with clay bars or Rain-X Bug & Tar remover. They are the spots that look like bird poo stains on my hood:
Any suggestions on how to get rid of them?
Try some rubbing alcohol and see what happens. I know it will do wet sap but don't know about dried sap.
Are you sure its not concrete? Saw that on a buddies car that followed a concrete truck too closely. Not helpful since I dont know of a way to remove them. 
I spray brake cleaner on a rag and wipe off. I deal with this all the time. I have a tree that sprays my cars with tree sap if I park it under long enough.
If they're dry/hard enough, you can carefully take a razor blade and 'pop' the sap off in chunks and then clean up with mineral spirits.
WD40 spray let sit wipe off. redo a few time it works and shines the paint too.
Regarding the concrete thing I heard on Car Talk last weekend that muriatic acid will take it off without damaging the paint. I'd still try it on the underside of the trunk or a door sill first, but hey, worth a shot.
I don't think it's concrete- this car's spent quite a a lot of time underneath trees. Thanks for the suggestions, I'll let you all know how they work out.
You may want to try turpentine. But check it on paint that doesn't show first to see how it affects the paint.
Shotgun?
Did you try threatening it?
^that's funny
Deep Woods Off! seriously works wonders. scrape the dried outer layer off with something that won't damage the paint, and then use the Off. It just dissolves the gummy sap away, almost magically. Well, pine sap anyway. YMMV depending on the type of sap you have.
Mist the whole car with olive oil before you park under the tree again. This simple precaution will make future sap removal as simple as wiping it off with a paper towel.
Hit it with a hammer.
I have always had luck with any sap remover I've used. How hard you have to scrub and for how long depend on how long it's been on there. Use any of the above recommendations and a bit of patience and you'll have a sap-free car in no time.
Invest in a car cover as well.
I've used a few methods with varied results. My best is plastic razor blades(of auto body origin) to get the big hunks, followed with rubbing alcohol and a Mr. Clean Magic Eraser.
Shotgun?
Mr. Fawlty's method may not work for you though:
