Life science workflow systems are developed to help life scientists to conveniently connect various programs and web services. In practice however, much time is spent on data conversion, because web services provided by different organisations use different data formats. We have analysed all the Taverna workflows available at the myExperiment web site on December 11, 2008. Our analysis of the tasks in these workflows shows several noticeable aspects: their number ranges from 1 to 70 tasks per workflow; 18\% of the workflows consist of a single task. Of the tasks used are 22\% web services; local services, i.e. tasks executed by the workflow system itself, are very popular and cover 57\% of tasks; tasks implemented by the workflow designer, scripting tasks, are is also used often (14\%). Our analysis shows that over 30\% of tasks are related to data conversion.