That isn't just an ordinary element name. That's a qualified name, meaning that it is a name that specifically refers to an element type within a namespace. The element type name is 'lat', and the namespace prefix is 'geo'.
Right now, jQuery can't deal with namespaces very well, see bug 155 for details.
Right now, as a workaround, you should be able to select these elements with just the local name:
$(this).find("lat").text();
If you have to distinguish between element types with the same local name, then you can use filter()
:
var NS = "http://example.com/whatever-the-namespace-is-for-geo";
$(this).find("lat").filter(function() { return this.namespaceURI == NS; }).text();
Edit: my mistake, I was under the impression that patch had already landed. Use Adam's suggestion for the selector, and filter()
if you need the namespacing too:
var NS = "http://example.com/whatever-the-namespace-is-for-geo";
$(this).find("geo\\:lat").filter(function() { return this.namespaceURI == NS; }).text();