Summary: If Logitech would improve the reliability of this it would be the very BEST trackball I've ever used. Alas, it does not seem likely. Do NOT buy this.
Pros: Comfortable, very usable, my favorite trackball by far (when it works).
Cons: Life expectancy is VERY short. They usually last < 3 months before problems show up. Left button begins double clicking on a single click, mouse stops moving cursor (and yes, it was cleaned carefully). Quite possibly the worst product Logitech has ever made - I have owned 7 of these things and am extremely disappointed. No scroll wheel.
Pros: Comfortable design Responsive trackball Wired USB
Cons: No physical scroll wheel SetPoint has no option for a good scroll wheel emulation and is all around awful to work with. No Linux support, I had to manually configure Xorg to emulate scrolling with the 4 button.
Summary: I would've expected the Trackman to just be normal Logitech optical hardware turned upside-down with some axis reversed in firmware with little consideration for what the consequences would be, but somehow they managed to screw up even the bits of such a plan that should've worked. Although it's too big to offer spatial advantages over a small mouse, its problems are ignorable for anyone uninterested in general-purpose pointer coordination.
Pros: Every Logitech product is, as near as I can tell, immortal.
Cons: The optical tracking is poorly implemented; the optical sensor itself is unable to track rapid movements and is situated at a 30 degree offset of where it should've been to maximize both responsiveness and finger mobility (as is, there's a tradeoff). The firmware does not iterpret yaw data to compensate for the offset, and crashed twice on me in six hours of usage.
Excerpt: Works perfectly with Win XP and Win Vista BUT "button 3" does not function as a "double click" button when used with Microsoft Word and/or Excel and Windows 7 operating system. Spent an hour with Logitech tech support - they actually went into their lab and tested the mouse with Word and Excel and verified - button 3 works with XP & Vista but is non-functional with Windows 7.