I am also thinking about it for the silent computer aspect of things. Granted, 8GB is not that much by today's standards, but for a basic web surfing machine...
I don't think that would be such a good idea. Well, the idea is good, but using compact flash cards for it is not. These cards wear off quite quickly because they can be written/rewritten only so many times. (and that number isn't *that* high). So when using them as a regular harddisk, the virtual memory would also be written onto that disk. I don't think any compact flashcard would last a lot longer than one month.
I don't know how the story is for those solid state harddisks, but I suspect they don't have that limitation. (would be pretty stupid if they did, no?