As another data point...
I use gerbv and really wish I wasn't. Major hassle with it is the lack of native file dialogs, so every damn time the thing opens, to get to gerber files I have to click, in turn, 'projects', 'xx-yyyy project name', 'pcb', 'xx-yyyy pcb name', 'outputs', 'Gerber'. Every bloody time it opens in the installation folder and since the dialog is not native it doesn't respond to any of the great utils that quickly get normal app dialogs to the folder of interest. I am just completely pissed off with having to manually navigate the folder tree using a shit foreign file open dialog.
Other than that, I guess it works. For copper - no holes or slots. Come to think of it, I have no idea why I am using this thing! Maybe I can find something better in an earlier post.