750,000 on my most detailed model, with lots of culling. Mid size ships are between 30,000 and 70,000, can have several dozen of these on screen during large battles
On low-end hardware (HD4000) my GPU-accelerated fractal algorithm for planets is set to draw just a little over a million triangles, whereas on high-end PCs it can be cranked to push over 4 million triangles.
Various other effects (particles effects, stars/parallax) render several thousand more tris.
For mobile devices (e.g. HD4000) in total I push somewhere between one or two million triangles (unfortunately this comes at the cost of pushing 1080p framerates under 20 fps, though 720p is still very smooth). On more powerful desktops with good graphics cards I can push 5+ million on 1080p with no framerate drops. I haven't yet tested this on any ultra-powerful desktop machines, my hardware is a little dated. I suspect some new machines could do millions more tris.
My game is highly GPU-bound in terms of performance, CPU makes little or no difference except for load times (NOTE: load times can be pretty awful for complex models on low-end machines).