Just to add my 2c worth.

My replacement at the company I just left hit the nail on the head. He
stated that he felt it was a question of critical mass. He then went on to
state that the firebird movement didn't have that. I don't agree with this
point of view at all.

I think to answer the question completely you have to look at the graph of:
1) downloads of the product
2) installations and the userbase it is supporting
3) active contributors to this and the other forums
4) number of developers who have contributed to the product (in terms of FB
devel).
For these you need to look at them over time (historically). That would
show the direction the product is going (growing or shrinking). I have been
involved in a certain products where you definitely get the impression that
the pond is evaporating. I don't see this with FB.

In two years time.... I think you have to do a risk analysis at the cost of
porting to another back end at date points in the future. For me right now,
I can always argue with my customers that if both Borland (for my Delphi)
and FB die a death our position is that we could sustain developments for at
least 3 years, giving plenty of time to port codebases and databases.

As to the commitment of the team that currently contributes, who knows what
will happen, I have yet to see a more committed bunch, but getting a long
term revenue stream would certainly help them, I'm sure.

JAC.