I am lucky enough to have an iPhone and whilst there have been apps previously they seem to have upgraded to being something that is really helpful.
I use the Ancestry app which now links with the online tree(s) I have and allows for updates / editing. I haven't really kept those trees up to date but now need to pull everything together.
I also use GedView which does not allow editing but gives details in a list allowing you to easily see all the who-evers you have, you can also look at the family groups but an alphabetical list has turned out to be really useful on many occasions.
Lastly I have recently donwloaded iFMP - I today looked up all the Caddies and put the details into my ONS. Very easy interface and gave me 165 Census returns, 56 Births, 33 Deaths and 55 Marriages. The BMD are all for England and Wales but some of the census returns cover Scottish locations (although I am fairly sure not all of them) - I now need to check online what their records actually cover.
The best bit has been to be able to update, check details when I am out and about - for instance I had to wait for my car to have a new exhaust yesterday, as it took much longer than expected I was able to use the productively.