lisa who previously submitted this hack, sent me a link to her "how-to-install-a-floating-lack-shelf" instructions. it's not a hack, but i've decided to post it because it's just so useful.
"i bought the ikea lack shelf a few years ago and i was freaked when the box didn't come with the shelf hardware. i had no idea what to use to put it up securely. a search on the internet had not helped, there were loads of horror stories of shelves crashing in the middle of the night and precious belongings being ruined. so when i finally did take on the task, i decided i was going to document it so i could help someone else. here is that post on my blog, feel free to use it if you think it can help your readers."