I got into BOG with my boyfriend yesterday on my birthday without a reservation. It was just the two of us so we have no problem with eating at obscure meal times (like a 4pm "dinner"). I had no reservations and tried so hard to get them but had zero luck. We got there around 3:15 and just hung out around outside in the blazing heat until they opened for dinner. Don't let the staff make you feel there is little hope. First they don't consider the walk-in line just that. To them it is a "cancellation" line and if you do get in, it is because someone cancelled. So it's more of a privilege than a courtesy. I highly doubt that i got in due to cancellations because there were tons of extra tables during the first hour of service. In beasts room alone, it was about 80% empty! They all have to say the same things: "we are booked for months through", "we won't know until we open at 4 if there are any cancellations" etc. but just ignore them and wait in the line outside on the left.
I got on around 3:40 and was first in line and they took my name, party number and gave me a pager when they opened. It was super easy and I was seated at around 4:15! I'm so glad I read about a similar experience on here and didnt completely rule out a chance to eat here because it was a wonderful dining experience..we even got to meet Beast in a room where there was only a tiny line of people because everyone was still eating!