I'm using the HTML5-only version of History.js, as hash-fallbacks aren't appropriate for our site architecture at the moment but we require normalization of behaviour in modern browsers. I haven't wrapped the script in conditional comments, so older browsers are still loading and parsing the scripts. I appreciate this is less than ideal but that's a separate issue with it's own reasons.
Currently in IE7 the HTML5-only jQuery version is throwing "'Undefined' is null or not an object" -- I'm using the compressed bungled version but it looks like line 30 of Core, i.e. JSON object isn't defined.
Does this count as a bug, or are conditional-comments the expected usage for older browsers?
It seems that the bundled js file misses the json2.js file. As a workaround you could add json2.js, history.js and an adaptor manually, that seems to work.
I included the json2.js before the bundled HTML5-only jQuery on IE7 (using conditional comments) and it started to work.