Have you ever been routed to the wrong version of a website - or denied access altogether - because the site thought you were in some other country.
It's usually because that's where your ISP is headquartered. Or logged onto the BBC site while you were abroad and found yourself being served adverts?
If so, then you were a subject - a victim, some might say - of geolocation techniques.
The upside is they're getting more accurate, according to Marie Alexander, CEO of Quova, which is one of the leaders in this area. She says that, as more and more websites use geolocation, pressure from end-users has pushed formerly sniffy carriers and network operators to open up to companies such as hers.
What they're revealing is the internal network mapping that geolocation needs in order to provide the best possible fix. That in turn enables websites to provide localised content - yes, including local adverts - while ensuring that the carriers' customers aren't wrongly locked out.
The downside is they're getting more accurate, so it is harder to hide your location. If, like one of my friends, you're a BBC licence payer who is (legally, but immorally) prevented from watching content you've paid good money for, just because you're in your French holiday cottage, it's not so easy now to work around it via a proxy.
Of course there's also honest reasons for blocking proxies - criminals have used them in false applications for bank accounts, for example. Alexander says that even proxies "have their own electronic signatures that can be correlated."
She notes too that the anti-fraud departments of financial organisations have got lots better in the last two years at correlating such information and looking for patterns that indicate possible fraud. (Some might add that it's a pity they didn't direct their attention inwards, as well as outwards.)
One of the biggest opportunities for geolocation remains mobile services, of course. While there's extra location data potentially available here - cell IDs, phones with GPS, Wi-Fi triangulation - it's often not immediately available though. Phones may need client software to provide a GPS fix, for instance, and then you probably want that software to be permission-based for privacy.
Amazingly, Alexander reveals that, while US E911 legislation requires the mobile operators to be able to locate emergency callers to within 300m, the functionality is often hidden and inaccessible to applications running on the phone.