> Is the 1.0.1 version of jaybird compatible with Firebird 1.5?

Should be. Issues might happen in the metadata handling, though should not.
The wire protocol code did not change, might be that we have fixed some bugs
since 1.0.1 there, though I don't think so.

> Are there any issues involve with updating to 1.5.6 or 2.0?

Upgrade from 1.0.1 to 1.5.6 should go smoothly. Upgrade to 2.0 might be
tricky if your application relies on one of the standard deviations that
were fixed in 2.0, e.g. looping through the result set and updating the
database using the same connection in auto-commit mode (see release notes
for more information).

Roman