We reached the Bolivian/Argentinian border around 7.30 in the morning, after catching a 4am bus from Tupiza.
There was a bit of a queue on the Bolivian side, to get an exit-stamp, and the tiny building was so poorly suited to the task of handling all the traffic that for a while we couldn't figure out where to go.
Once we got that sorted out, got our stamps, we crossed the bridge over to the Argentinian side. That is where the fun began.
First we queued for an hour and a half, to get our passports stamped. While waiting, we watched with confusion as border guards picked people at random from the queue, took their documents and sent them to another queue, to have their bags searched. They would then return with the stamped documents a few minutes later. The confusing thing was, that apparently many people wanted to be searched, shouting at the guards and demanding to be moved. Weird.
After finally getting our stamps, we realized why: everyone had to be searched. After standing patiently in one queue, not arguing with anyone, we were rewarded for our coopertation by being sent to the end of the other queue, while the pushy and greedy and lucky had long since passed us by.
It was really quite infuriating - our first day in Argentina wasn't off to a very good start.