Well, I finally found the "right person" who could get me onboard with Sametime United Telephony. (Of course, I found that person at Lotusphere!) So, I sat down to enable SUT on my Windows 7 desktop. All went according to plan until I actually made an inbound test call to my SUT number...it worked once, then everything failed. It went beyond just SUT; I had no audio in any application, no calls, nothing.
A bit of digging led me to the Technote linked below. As it happens, Windows 7 makes a distinction between "Default Device" and "Default Communications Device" in its sound configuration. Since I had not specifically named a default communications device, SUT was grabbing the speakers and microphone of my laptop; this, in turn, created exclusivity problems (which explained why no other apps could use the sound devices). As far as I can tell, this issue would affect any softphone under Windows 7. After digging up my Bluetooth earpiece and configuring it as my Default Communications Device in Windows 7, all was well; I'm placing and receiving SUT calls with no issues. I just thought I'd throw this information out there in case anyone else is being bitten by this somewhat hidden Windows 7 gotcha.