Having read more descriptions of multitasking in forums etc, I actually think it may be more RAM-intensive than I originally thought. The three official categories of app that can keep running in the background, navigation, VoIP, and audio streaming, can all be pretty light on RAM (well, the last two anyway - with navigation it depends), but the fast-switching, put-an-app-on-ice-and-return-to-it-right-away multitasking for other apps would eat up a lot of RAM. And the iPad is in inherently worse shape in that regard because all of those graphical effects / layer blends / etc on iPhone mean there are a lot of copies of things on the screen being stored in RAM; a 1024x768 uncompressed image with an alpha channel is 3 MB, so it doesn't take too many of those to make a dent in the not-particularly-large portion of the system's memory that's reserved for application use.
That being said, the iPad seems to be able to open up a fully-loaded copy of Pleco in under a second, so once we've got a few more updates under our belt and we're at a point where we can perfectly restore the previous application state on reopen, you may not find you miss multitasking on it much for Pleco at least.