When I run out of free tiles (which is happening more frequently these days due to popularity of the site) it is frustrating. So I'm thinking of displaying Open Street Map data instead (only once all the OS tiles are used up for the day).
Free online Ordnance Survey maps showing footpaths, etc.
This is the Google+ page for the footpathmaps.com website where I will announce new features and where you can request features or give feedback. Footpathmaps is a free OS map viewer allowing you to identify public footpaths and bridleways.