I currently have two 235s and have noticed significant differences between the backlight, mostly the spot at the bottom and how even/uneven the lighting is across the screen. There's clearly a lot of variance in Garmin's manufacturing process.
Here's the comparison, though hard to exactly capture what the eye sees...
Although both show the spot at the bottom, for the one on the left the lighting comes across as very even across the screen to the eye, whereas the right is noticeably brighter in the lower middle (i know this doesn't show up quite as much here - damn iPhone camera! - i tried to be as fair as possible when taking it). It really stands out when you have more white in the middle (e.g. data fields when running).
And another angle to try and capture the differences...
Note that although i've sharpened the angle here the angle is still not that extreme. The spotlight effect is really there, and visibly different to the eye between watches. And depending on your level of OCD can be really annoying (especially when you've just paid $100's of dollars for the watch).