That is a such a simple formula, I never woulda thought of doing it that way! Nice! It also confirms a handy rule of thumb I discovered: take your eyeball-to-screen distance and divide by two. That will give you a ballpark figure of what size (diagonal) screen to look for. Worked great for me: I'm 100 inches away from my 50-inch TV. For SD, it's a tad soft, but for HD, it's just a wee too small -- a good balance, since I watch both.
Athena 2 x AS-B2, 2 x AS-C1, 2 x AS-F2 speakers; Logitech Harmony 676 universal remote control; Monster HTS 850 home theatre powerbar; Oppo BDP-83 universal player; Scientific Atlanta 8300HD PVR; Sony SLV-N750 VCR; Sony SXRD KDS50A2000 HDTV; 1 x SVS PB10 subwoofer; Technics SL-1700 turntable; Yamaha RX-V750 receiver