That's an interesting way to distinguish the words, but that's not an actual rule in the English language. The only usages where "while" and "whilst" are not absolutely interchangeable would be if you're going to go outside for a while to while away the time. You would never go outside for a whilst to whilst away the time. As a conjunction, they mean exactly the same thing, are exactly the same part of speech, and the difference is purely dialectical.'Whilst' is an adverbial genitive. This means it is used to describe verbs.
For an example of where it's used, in English English at least, 'Whilst rising, the sun shone'.
Not used as 'Whilst the sun was rising, it shone'. 'While' would be used instead here.
In writing, I always use whilst, but I don't really remember ever saying whilst until 5 mins ago whilst debating it with my girlfriend. I just know I've always used it that way. Maybe it is slightly dated now though. I'm only 23, I don't want to sound like something out of Shakespeare.
I usually tend to use it when writing formally or writing essays, not when writing my thoughts on a random forum! Sorry to bust in on this, I just want to set the world straight on it now!