Not being able to get out of the saddle easily also means making much more use of the gears, which I'm not really used to. We lose speed remarkably quickly and pick it up remarkably slowly.
Pretty much sums up my experiences with tandeming too, you really need to keep on top of the gears.
That was one reason I tried hard to get STIs on mine - too much shifting to be dealing with downtube shifters! Quick descents and then short ascents are a pain too, I can't find a good gear and it's so difficult to 'feel' whether you're picking up the bike or mashing your stoker's knees...
Pretty much sums up my experiences with tandeming too, you really need to keep on top of the gears.