Giving a (software) product a numeric usability score is a thought I had in many of my past projects. Having a final verdict in form of a %-value or a grade would give me a certain comparability between projects and some customers would prefer this kind of "certificate" over (just) an elaborate text. While for full reviews I still prefer the qualitative, informal approach, this formal summary could be applied when a full review isn't demanded.
Userfocus.co.uk has a nice example for this; guidelines can be checked (3-tier: doesn't comply, complies and kind of complies) and the XLS will promptly output a %-score for all of the 9 topics, together with a beautiful spiderweb-chart.
I gave it a try on my companys website. My impressions were mixed, it did provide some tendencies where the main problems are, but the statistical value was very dubious in my eyes. Some of the topics had only few checkpoints relevant to the website and some of the questions were highly subjective to anser. E.g. the topic "Forms & Data Entry" has a full 100% but mainly because only 6 of 23 answers were given.
What do you think? Does this quantitative approach has any value for evaluation? Could it be done right to get a meaningful and statistically valid outcome?