I've just installed it (to My Documents - doesn't require any permissions) and it and the extensions work a treat (the extensions weren't available on the previous portable version). The extensions I've put in are the ones I already have at home on the the full version - Chromed Bird, Google Mail Checker, Diigo Web Highlighter and Bookmark, and RSS Subscription Extension (by Google). I've also added ChromeMilk - but I might just keep that as a tab to the full site on my home pages. I should probably find one for RSS too. Any other suggestions?
So, thank you to Jo, and thank you to the nice people at PortableApps.