I sell 64MiB VPSs and there has been a lot of internal discussion on the subject; should we continue selling them? As the article says, if you are willing to put in the work, even 64MiB can be useful.
On the other hand, more ram gives you a lot more breathing room. It is much easier to do useful things if you get the 128MiB service instead of the 64MiB service. (I charge $4 per account, and $1 for every 64MiB ram, so 128MiB is only a dollar more a month than 64)
Nick, an employee of mine, points out that the 64MiB guests are still useful because they force people to learn about every process running on the box, and to only run what is absolutely required. And he's right; that is a great thing to learn. But it is also a lot of work.