Tweaked the data number RegExp some to handle some other edge cases.

src/data.js

 (function( jQuery ) {
 
 var windowData = {},
-	rnum = /^-?[0-9.]+$/;
+	rnum = /^-?\d+(?:\.\d+)$/;
 
 jQuery.extend({
 	cache: {},

test/unit/data.js

@@ -158,7 +158,7 @@ test(".data(String) and .data(String, Object)", function() {
 });
 
 test("data-* attributes", function() {
-	expect(20);
+	expect(22);
 	var div = jQuery("<div>"),
 		child = jQuery("<div data-myobj='old data' data-ignored=\"DOM\"></div>");
 		
@@ -184,6 +184,8 @@ test("data-* attributes", function() {
 		.attr("data-false", "false")
 		.attr("data-five", "5")
 		.attr("data-point", "5.5")
+		.attr("data-pointbad", "5..5")
+		.attr("data-pointbad2", "-.")
 		.attr("data-null", "null")
 		.attr("data-string", "test");
 	
@@ -191,6 +193,8 @@ test("data-* attributes", function() {
 	equals( child.data('false'), false, "Primitive false read from attribute");
 	equals( child.data('five'), 5, "Primitive number read from attribute");
 	equals( child.data('point'), 5.5, "Primitive number read from attribute");
+	equals( child.data('pointbad'), "5..5", "Bad number read from attribute");
+	equals( child.data('pointbad2'), "-.", "Bad number read from attribute");
 	equals( child.data('null'), null, "Primitive null read from attribute");
 	equals( child.data('string'), "test", "Typical string read from attribute");