Most of the more recent iLo stuff has been pretty crappy. I bought an iLo 3200 over a year and a half ago. Has always been decent to me with the exception of the clock gaining time (has been that way since day one). The backlight uniformity and total lack of flashlighting (brightness in corners or spots as you're seeing) actually make me happy that I chose it, most stuff out there today is much worse in either respect. It all depends on who they're sourcing stuff from. I'm sure there weren't many 32 inch panels they could source from back in 2005, so what they got was probably halfway decent, get an excellent viewing angle and good overall performance. Problem is what held true then doesn't hold true now. 32 inch panels are much more commonplace and hence it's probably easy to make a cheaper junkier set then it was a back then.
Since then they seem to have been on a downward progressive spiral however. The earliest weren't half bad, but the sucessors have been pretty much junk. The iLo 32HDs which were the sucessor to the 3200 and subsequent ones have motherboard issues and a few months down the road it no longer can switch sources, adjust the volume etc. These were Initial sourced sets in various sizes. Some however were sourced by other companies (such as whoever is making the Akais in the 32/26 inch size range). The 42 you have seems to have issues with the sound however if its working now you're probably in good shape. I've not heard of many other complaints about it.
The 42 inch Plasmas were all over the board, the very early ones (Mexican assembly) were OK, then the Tatungs followed and they were pretty unreliable thereafter.
I'd just as soon take it back. Even if they're charging what they're charging around here I'd still avoid it, there are decent sets for not much more. If you got an insanely good deal then you put up with its flaws (I know such deals are out there, two of my HD sets came from deals that were almost too good to be true). So don't get me wrong, I'm happy with my iLo, but today's iLo isn't the same as yesterday's, and tomorrows will probably be entirely different again, all depends on who they're sourcing it from.