Spazure Silicon blogged this tip on his/her blog with the caveat that "So, even though this formula won't ever be on the CRM Best Practices Custom Formula blog, I hope somebody finds it, and finds it useful." So, mainly to prove him/her wrong, but also because it's very useful, here it is - a function to convert Date/Time into HH:MM:SS.

This particular formula was designed for cases, calculating the elapsed time in HH:MM:SS between right now and the time the case was created. As you see, I had to use the TEXT() function to convert the numerically output Date/Time function results into text, which were then fed into the Concatenate function to make everything display nicely on one field. My original version of this formula actually used multiple fields, {!Hours} {!Seconds} {!Minutes}. This made the final formula look prettier, and helped with debugging, but ultimately was impractical for distribution.

So, even though this formula won't ever be on the CRM Best Practices Custom Formula blog, I hope somebody finds it, and finds it useful. If you use my formula, please comment -- not because I want credit, but because I really do like to know where my code ends up. :-)

Text(FLOOR((NOW() - {!CreatedDate}) * 24))

&":"&Text(FLOOR(((NOW() - {!CreatedDate}) * 24 - FLOOR((NOW() - {!CreatedDate}) * 24))* 60))

&":"&Text(FLOOR((( (NOW() - {!CreatedDate}) * 24 - FLOOR((NOW() - {!CreatedDate}) * 24 )) * 60 - FLOOR(((NOW() - {!CreatedDate}) * 24 - FLOOR((NOW() - {!CreatedDate}) * 24 )) * 60 )) * 60 ))