According to http://www.percona.com/blog/2007/08/28/to-sql_calc_found_row... (which is a very old thread and may be completely outdated), it's also often much slower than just doing two queries.
Although, like you said, that thread dates back to MySQL 5.0 - I wouldn't hedge my bets on it today...
Is there a "best practices" way to handle pagination of complex queries without running the query twice?