Did anyone here ever printed any black and white comics via Lulu.com? I'm having some difficulties getting my book to come out right and I'm suspecting that the people at the forums there never even tried to print anything like it before. They actually told me to use JPG files instead of PNG :/ That sounds like a terrible idea!
Any tips? Something? Anything? I could really use some help here from cartoonists.

What exactly is off about the printed book? JPEGS saved at maximum quality are actually fine. I wouldn't use them for offset printing of course but for PoD they're adequate. Make sure they're grayscale since your book is black and white. I suppose you're uploading a pdf though, as the site requires; are you placing pngs inside the document and then exporting the pdf? I have no idea how a pdf exports pngs, but if there's a conversion occurring, it can't be good for your final files. In that sense jpegs are safer, but Id like to hear from someone who's more familiar with this. I've never used PNGs inside a document meant for print, I usually export direct from PSD in general, and jpeg for lulu.
I use Lulu a lot for my tutorial books and other things; the only time I wasn't satisfied with the result was when testing their cheapest printing option, which is not made for artwork at all.

Well, the whole thing just didn't come out dark enough. Some of the bright stuff has just vanished! I just ordered a smaller test book of the same book with a bunch of different files (PNG, GIF, TIFF and JPEG) in different variations, but all of the same pages so I can actually compare results. I picked specific pages that printed especially bad before, and some others that are just random. I think I'm going to learn quite a bit from that.
Another problem I had was that they pushed everything down by 4mm, thus making the bleeds at the top of pages completely pointless and creating a white margin at the top of every page. I'm not sure what to do about that other than yelling at the Lulu printing staff... which are obviously at fault here. They completely ignored their own specifications. I understand there's a margin for error, but not that big a margin!

I see, that's really strange. Regarding the black, here's a trick for what it's worth, but it's used for offset printing, I don't honestly know how it it will work for PoD: you could try converting your files to RGB and your black to a rich black (I guess R0G0B0, though we usually do it in CMYK and the default for that in Photoshop is C75M68Y67K90). This is because printing pure 100% K always looks lighter on paper, so it always needs to be overprinted with other colors to be properly black. I hope this can help somehow.
The layout thing though, that's a bitch and clearly their fault!

I'll try the RGB thing. It might just do the trick. Thanks.