> >Huh? Sorry, this sounds like some random FUD. Neither GPL nor IPL
> >imposes any restriction on usage of covered software.
> I'm really sorry, but the document you references states definitively
> that linking object modules subject to IPL (and by extension, IDPL) and
> GPL is "illegal". While Firebird doesn't presume to say how you can use
> the code, the Free Software Foundation most decidedly does.

Not quite. As stated in section 0 of GPL "Activities other than
copying, distribution and modification are not covered by this
License; they are outside its scope.". So you can use any combination
of GPL and IPL software, as long as you do not distribute it.

> >Actually, Firebird does (or should) care. Incorporating IPL-covered
> >code into GPLed work does violate IPL just as well as the reverse
> >violates GPL. So the licenses are incompatible in both directions (as
> >opposed to, say, revised BSD license which is one-way compatible with
> >practically anything).
> I think you will find nothing in the Firebird or IBPhoenix archive that
> suggests that Firebird or IBPhoenix has the least problem with linking
> Firebird with anything or everything. The source of the restrictions,
> prohibitions, and threats are solely from the "Free" Software Foundation.

To the contrary, I do not even need to search:
How about
http://www.firebirdsql.org/index.php?op=doc&id=idpl
which in section 3.1 clearly states "You may not offer or impose any
terms on any Source Code version that alters or restricts the
applicable version of this License or the recipients' rights
hereunder."?
Also, right in this thread someone posted this: "For the record,
Netfrastructure code that 've donated to Firebird has a proviso that
it can't be re-issued under other licenses" and then this: "I wish to
exclude developers who wish to exclude developers".
So, at least one developer clearly has some problems with linking
Firebird code with GPLed code ;)

> To the best of my knowledge, the only reason that IPL/IDPL "violate" the
> GPL is that they don't requirement software developers give away their
> work for free if they don't wish to do so.

This is only half the reason -- the other half is no-relicensing
provision mentioned above.