I just had to use the wp34s conversions in "real life" for the first time yesterday, and I had a problem with the user interface.
Basically, I had to convert a few values from cm to inches. I entered the value, entered the Conv menu, chose the appropriate conversion, and read the result on the display.
Then to convert the other values I had to do it all again, because if you try to enter another number, the calculator just changes units, keeping the same argument, until you press Enter or Exit.
Now, in real life it never happens that if, for example, you need to convert 12.34 cm in inches, then you have to convert 12.34 lbs to kg or whatever; it's much more likely that if you are converting cm to inches, you will need to convert more of the same units.
So I would suggest the following modification: you enter the Conv menu, choose the units, then press Enter to acknowledge the actual conversion you need; then you can repeatedly enter arguments and they are all converted, without the need to re-do everything from scratch.
Then if you press Enter twice, the calc could exit the conv menu leaving the latest value on the stack; or pressing Exit would just exit without modifying the stack.
What do you all think? I think this (or something similar) would be much more user-friendly in "real life" than it is now! :)
Cristian