Customs duty threshold in Germany is something like €20 for the total price including shipping costs. If you go higher, you've got to pay 19% VAT on the total price.
Once you go over €150, there are additional customs charges depending on the type of item.
If you choose standard shipping, you might or might not receive a customs slip first, for collecting your item from the customs office and paying the fees. Chances of getting stung have been 50/50 for me if an item happens to exceed the €20 threshold.
However, choosing express mail service (EMS, DHL Express, etc.) often stings you with additional handling charges you've got to pay to the mailman.
I bought my girlfriend some Zelda spiritual stone necklaces from Sanshee.com (US) last year, total amount was €60 including DHL express shipping. Dumb me, thanks to the express service, DHL collected the 19% VAT plus the handling charges right at front of my door, which meant spending another €30.