I just realized -- the examples you linked to are taken by the creator of Pinhole Designer, he has a head start on some of the rest of us!

You can survey a few of my pinhole efforts on my PBase gallery site. The film images I took for WPPD 2011 (with a completely homemade 4x5) suggest it's my best homemade pinhole yet. My attempts with paper negatives indicate a little more tweaking, especially an adjustment of the pre-flashing, might be useful.

So far, a body cap adapter for my Bronica, getting 6x6 cm format exposures, is the smallest format I've tried, so I don't have much feel for what 35 mm might do. I second the recommendation for Acros, as there are enough complications without adding large reciprocity failures.