Are you talking about the SWFs running slow, or the Flash authoring environment running sluggish? I can't say that I've ever experienced a flash file running slowly becuase of text (and I've put some absurd amounts of text in flash at times), but I have experienced working on the projects grinding to a crawl from having a text box with a few hundred lines of text in it.
I'm filling a need. Without me there would be no bad examples.
nope, not the swf running slow, just flash itself. and it doesn't seem to matter if its a lot of text or just a few lines, but for some reason it makes flash very unresponsive, even doing basic things like selecting layers and scrubbing in the timeline.