Hi Dave,
There is stage view which you could use on tablets.
Stage View uses the web browser on the device, so in theory it will work with any device which has a webrowser and can connect to wifi, or the internet. So this SHOULD work on laptops, iPads, Android Tablets, Blackberry playbook, HP's webOs tablet, phones and maybe even PS3, XBOX, Wif's and Smart T.V.s (not I havn't tried all these out ;-)
The only issue I can see is that a tablet may be to heavy for frail people. However I should imagine that due to cost propel who would want to use this would bring their own tablet along!
It would be nice if my church could afford tablets.
For more info see: http://manual.openlp.org/stage_view.html