I've hit a recent change which took me by surprise.
I was used to checking for the 'questions' global status variables to see the total amount of queries the server performs. So, for example, I could run com_select/questions to learn the SELECT ratio out of all queries.
Apparently, as of 5.0.72-5.0.76 & 5.1.31 this has changed. A new status variable was introduced, called 'queries'.
The change being? questions does not any longer indicate the number of queries the server has executed: only the number of queries requested by the client (so, calling on a stored routine only counts as 1, regardless of how many queries the routine executes). The new queries variable indicates the amount of server queries issued (see the 5.0 and 5.1 docs for details).
So, as of 5.0.72 or 5.1.31, the calculation should be com_select/com_queries (or com_select_diff/com_queries_diff) to learn the SELECT ratio of all queries. I learned this due to a bug report on mycheckpoint, which presented some 10265% SELECT ratio...
My take on this is that it could have been worked out differently: instead of changing the meaning of an existing variable, questions could have remained as it was, with the introduction of, say, client_questions, which would only indicate client number of issued queries.
I believe changing the meaning of status variables at such late versions (5.0.76 is quite late!) invites trouble: code that used to work on already then-stable versions (e.g. 5.0.51) would behave differently after upgrade. Such changes should best take place while still in BETA phase.