I'm Shure someone here knows this :>)
Would it be ok, 'safe, to have the SATA cable (and power cable) disconnected at the drive end but still connected at the PC? 
I sometime use a second b/u drive which I'd like to just disconnect when it's not needed, but I haven't found an answer for this in google searches.

Yes.  I do that at times.  I don't disconnect the power, just the SATA cable, but if its going to be a long time you could also disconnect the power. 

   Hello... Yes it will work, but safe, seems to be subjective to who, when, how and the lawyers, these days... The safest way would be a HOT-PLUG Drive Bay for your case... a ONE cable device would be called e-SATA, and is designed for the repeated plugging and un-plugging of drives, they have better cable shielding, as Standard and internal SATA cables are not designed for repeatable and flawless keyed connections...
   You might want to find the internal SATA connector type that has the Power Plug molded together with the SATA flat cable, at the Drive end, for a "safer" repeatable keyed connection, they still can be found on-line and at your local computer re-cycler cable bins.
   You might have to tell your Windows version, that a drive is a "hot plug device", or "hot plugging" is enabled in your security settings. And be aware that repeated use of the internal type SATA connectors is 'NOT' the best or robust solution over time... But it IS much cheaper and faster DATA transfer than USB connections.

Thank you that was exactly what I was looking for, and yes caddies' are in my future..
 Ironically or not I had been using an external usb caddie for the one less used '2nd b/u drive. The #1 was the one happy sitting in the case. It's was the usb's speed moving big chunks that prompted moving it to SATA.
I found out last night though- stacking' them in the case like that weren't too cool. -the bottom one got shall we say.. a bit hot' LOL.