So far, so good!
Hola, just arrived in La Paz, have cleared immigration, and already checked into the Wild Rover hostel near Plaza Murillo. Waiting to see if this is a loud party hostel before I commit to more nights, or move to another one. So far this one seems fine.
This was my experience: it was a little faster getting through immigration since I already had my visa, but I did NOT need it before arrival as was posted on some official Bolivian sites. You can get the visa on arrival no problem at all.
I asked the immigration officer about that announcement of the visa being necessary before travel and he said that was NOT true.
Also, I was never asked for yellow fever vaccination from anyone. Not at the Bolivian consulate in Houston, not at American Airlines checkin, and not upon entering the country via La Paz airport. No one has mentioned anything about it at all.
Regarding altitude sickness, so far I feel fine. I felt slightly breathless upon arrival & am getting a very mild headache, but mostly feel just fine. I gave not had any mate de coca yet. The reception here at the hostel said that if you're going to be affected by the altitude, it usually happens right away as soon as you get off the plane. I did see one fit girl in her 20's get sick and vomit just as soon as we entered the first corridor. One other person looked sick also, but most of the people, including myself, appeared normal.
I didn't drink any alcohol, drank plenty of water, orange juice, tomato juice, and started taking ginkgo biloba 5 days ago (80-120 mg twice a day). I don't know if that helped or not. So far I feel just fine. :)