"Never buy anything without researching it," I smugly tell people. "Even the most well-respected brand can't be trusted to produce consistently great products." So what did I do today? I trusted a well-respected brand and it gave me the middle finger.
When my trusty Logitech MX500, an excellent wired mouse, died this morning, I grabbed the $70 VX Nano, forgetting something important they don't tell you on the box: it doesn't middle click.
Clicking the scroll-wheel merely changes the sensitivity of the scroll-wheel itself -- a physical mechanism, meaning there's no option to reassign it in the Logitech Control Panel. If you want to middle click, you have to reassign another button, such as the uncomfortably-placed rubber nodule under the scroll-wheel.
Why replace a standard and essential feature with a pointless trick? Logitech's mice used to be great: that MX500 lasted half a decade! Now its own support staff don't even know basic details of how their products are constructed.
Update: I took the advice of commenter maoinhibitor below to try the MX518, Logitech's own updated version of the one that died. Once again, I suffered research fail: there's no drivers for the Mac! It isn't detected by the Logitech Control Center, meaning that the buttons can't be assigned, nor the tracking speed changed. There's a $20 third-party app called USB Overdrive that fixes this, but I'm thinking "No."
Update 2: Of the third-party mouse driver apps, Steermouse is the only one that detects all the buttons on the MX518 under Leopard 10.5.2 and above. The others don't seem able to override the defaults for buttons 7 and 8.