Interesting! Can you tell me what version of Pierogi you're using, and if there is anything special about your N900? If you can actually see the IR lighting up, I can't see too many things that could affect it.

Let's see... I know that if you're running the LIRC server (which is used by apps like QtIrreco and Raemote), Pierogi won't be able to use the IR, because LIRC doesn't like to share. I suppose if you're running a special Kernel, Pierogi might not interact with it correctly. It might also be possible for very high or very low overclock settings to affect the signal timings, although I doubt it.

Also, some N900s don't seem to have as great a range as others. You might try holding yours right up to the TV's IR receiver to see if you can get it to work.

And, finally, let me note that while there are many keysets now in Pierogi, I make no claims that it can control every IR device out there. I think it's quite possible to still find a large number of TV sets that Pierogi does not work with.