Ok, here's how it went for me at Malko Tarnovo, passing from Bulgary to Turkey. I am a EU resident, so that may make a difference compared to non-EU riders. At the Bulgarian side, there are three stops. First guy checks my passport and bike registration, then passes me a USB stick. Next stop, another guy checks my passport and registration, has a bit of a chat with me and does something to the USB stick and hands it back. After that, a lady at the last booth takes the USB stick and you're off. To Turkish formalities that is.
On the Turkish side, you have to go through the system. First, get your visum. The price depends on your nationality, for me it was 10 euro. The guy at the desk just waved me away acting annoyed when I tried to pay with leva. He apparantly only likes euros of lira. There is an exchange office in the same building, where I exchanged my leva for lira. Even lira extracted a big sigh from the visum-guy, but he accepted the 20 lira (which is roughly 10 euro) and gave me my visum stamp. With that, you go through passport control. They stamp your passport, after which you go to the vehicle registration desk. This guy checks your registration ánd insurance so make sure you have both papers ready. If all is well, he gives you your second stamp. Then, on to the customs desk. This guy is supposed to check your bagage, but in my case he just looked at me and gave me stamp number 3.
With three (3, very important!) stamps in your passport you can drive on to the last post, which is the actual border. This guy wants your passport and vehicle registration again and shouts something back to this colleague. If they come to an agreement you are waved off and in Turkey!

Now I realize this may not be relevant to everybody (no insurance hassles and a EU resident) but maybe somebody finds it helpful.

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www.vincentkemp.nl 2009-2010 Prudhoe Bay to Ushuaia on a red '00 Honda Transalp