Not too much discussion of Air Niugini on these boards, nice to talk shop here... Here's my take:

1) With a limited fleet, any issue with any aircraft causes huge delays. Bummer, but it happens. As for reimbursement, I've seen them go both ways with hotels, transportation, and food. Be glad when you get your reimbursement!

2) See above... And referencing your PNG Air post farther down, I've found them at least as delay prone as Air Niugini. For intra-PNG flights, I've gotten together with colleages and chartered flights before, when delays get out of hand. Or to get to an airport with poor / no airline services. It's pricey, but you don't need pressurized jet or anything. Lots of bush planes are reasonable if you're not going too far from POM (Mount Hagen, Goroka, etc). And as always, everything negotiable in PNG. Not always an option, though. And many destinations are ONLY served by PNG Air, since Air Niugini got rid of some of its mountain routes.

3) I like their business class, and purchase on available flights. On the short hops, many times you're completely alone up front, so it's nice. Not used the auction, but usually there are plenty of empty seats on the international flights, too. So yes bid low!

4) Port Moresby is a difficult airport to deal with, yes. Leave plenty of time, and be patient... And lots of disputes there, I don't always feel safe there. Better to get to the gate or to lounge. And yes, long lines everywhere.

With all the issues, PNG is pretty beautiful place, from coastal areas to the highlands. No country quite like it! Always leave with plenty of interesting encounters and stories.