Of course, that's only true if you're using a totally flat heap. I don't see any reason why you couldn't be a little more clever about using a hybrid GC approac

Of course, that's only true if you're using a totally flat heap. I don't see any reason why you couldn't be a little more clever about using a hybrid GC approach (generational + thread-local allocation pools, for example) to minimize the size of the dataset that had to be paged in or out in a given sweep. RScheme and other persistent language implementations have certainly been able to use the underlying OS paging mechanism pretty efficiently, and the performance numbers Varnish HTTP cache seems to suggest that it can work well for some kinds of web application workloads, too.