A couple of years ago we saw an ingenious DIY (albeit for very able diy'ers). The people moving into our old office brought in a mid century craigslist credenza, cut a hole in the top of it and dropped in an Ikea sink to replace the practically prison style sink that had previously been in the office bathroom.
It took 3 guys and some very careful drilling and sealing (and someone familiar with plumbing) to put the whole thing together, but we loved the ingenuity of reapropriating a piece of furniture normally meant for an entry way or living room and putting it into the bathroom. It was also a more affordable version of getting a 'custom' cabinet plus it had a cool mid century look that matched the rest of the space. Of course it's only affordable as long as you have the skills to make it happen and it helped that they didn't need to rip out any existing cabinets, just unmount the sad little sink from the wall.
Have you seen anyone do this? Have you done this yourself?
Image from Siskin Valls