Fantastic! Very funny.
The random midnight, while initially helpful for finding things, gets annoying when you're trying to find those last few items - you needed to hide a "midnight-generator-switch" somewhere to turn this off (and off course you can't use it till you have all the blue coins - like a reward).
That picture is huge! Respect.
Didn't have any problems (no lag - but then again, I don't use a computer from the stone age) - just took ages to find 19, 28 and 29 (no medal for a sneaky-peak to get a hint for the last two!!)
One thing I thought was a shame - it would have been nice AFTER finishing to be able to have a look at the whole picture (zoomed out?) (without anything happening - like that random midnight). It is a great picture after all!