I actually thought I'd already blogged about this, but maybe I've just seen it in lots of other sites, that's all! Also, there are so many similar applications now (which is good) that it's hard to keep track (which is bad)... This one is called Geominder:
"Geominder allows you to create location-based reminders that stay attached to physical locations. When arriving at a marked location, Geominder can play an alarm and display a stored text note or a voice note previously associated to the location."Hmm, not sure how this could be relevant to tourists, as they don't really have a daily routine within certain areas (as opposed to locals who live and work in a particular city), but perhaps if the reminders could be shared between different devices, they could alert their friends to particular points of interest? That's just going back to the whole digital post-it note idea though, anyway...
I guess one possible situation would be if they saw something they wanted to buy, but wanted to wander around and compare prices first, then they could set a geominder at that particular shop, so when they walk past, it'll say 'hey, remember to buy this sheepskin rug here' or something like that? Otherwise, this doesn't seem particularly suited for travellers. =\