Since MOSS 2007, SharePoint workflow statuses display with a text value such as “Canceled”, “Completed” or “In Progress”, but behind the scenes are stored as a key with an integer value.  So in a view when you want to filter based on the workflow status you must use this key value, and not the display text.

As an example, here’s what the Filtering section would look like if I were filtering out items where the workflow status were either “Completed” or “Canceled”:

Here are the values and definitions for each workflow status, which still apply in SharePoint 2010:

• 0 – Not Started
• 1 – Failed On Start
• 2 – In Progress
• 3 – Error Occurred
• 4 – Canceled
• 5 – Completed
• 6 – Failed On Start (retrying)
• 7 – Error Occurred (retrying)
• 15 – Canceled (defined but not used)
• 16 – Approved
• 17 – Rejected

Hope this serves as a quick reference, it will for me!