There is a thread on enwiki WP:VPT [1] speculating that the sluggish server performance that some people are seeing is being caused by the dumper working on enwiki.
This strikes me as implausible, but I thought I'd mention it here in case it could be true. I suppose it is at least possible to expand the dumper enough to have a noticable effect on other aspects of site performance, but I wouldn't expect it to be likely.
-Robert Rohde
[1] http://en.wikipedia.org/wiki/Wikipedia:Village_pump_(technical)#Slow_Server