Well, that may be because the HP uses RPN entry along with a stack. I know that once you get used to it, you never go back. But that may be the geek in me. :)
By the way, my web calculator thingy has a page for a few of the common unit conversions.
I guess that means I'm a geek too then. I don't know how I'd live without my HP 48GX. :)
I have a hard time operating any other calcs that don't use RPN. I've got a 48GX at work and my wife's 48SX here at home. We're both EE's, so we have a double geeky household.