A popular method in some IRC fora when seeking design feedback is to generate gerbers for a design and post them to a website such as:
Then post the link,
Gerblook's backend is gerbv, and does a pretty good job of rendering layers.
IIRC, there may be an issue with slot rendering as it is an older version of gerbv, but otherwise it is a handy means of making a design available for review by many.
You generate your gerbers, zip them, and upload.
It is worth having gerbv on your own system to review gerbers as well, before sending them off.
gerbv will sometimes show things that aren't obvious in the PCB layout tool.
Incidentally, an acquaintance who used to work for a large electronics company in PCB fabrication talks about his "rule of 4". You'll spot 4 errors in your layout once the board has been made
His other pet gripe is the use of traces that are un-necessarily thin, wasting etchant and resources during manufacture.