The fact that this thread started in 2004 and it now is 2017 implies that this is a problematic expression. After reading some of the comments, I see three possible meanings "all but" can have, on top of the two standard ones.

Using a boxing metaphor "all but lost" could mean:

1. "All except": He has taken and given a lot of hits, fought hard, but not lost. => He hasn't lost.

2. "Nearly": He has taken a lot of hits, is fatigued, not quite lost, but is at the brink of losing. All possible negative things that could have happened have, except losing. => He is close to losing.

3. "Not at all": He has taken and given a lot of hits, is fatigued, but he surely hasn't lost. => He's not close to losing or is winning.

The third sense is not in dictionaries, but that's how I understand it in some contexts. "-That guy is such a loser. -He's all but a loser." => He could be a horrible person, a retard, etc., but he surely isn't a loser.

Technically, the listed senses might be the same, but the emphasis is different. What's the status of the boxing match? Is it (1) unclear, (2) moving towards a loss, or (3) definitely not moving towards a loss/moving towards a win?

I may not be entirely accurate in how interpret where the emphasis is, but my point is that the emphasis is different between the three sense.