There was a noticeable difference when I messed with the settings. If I set it to something it didn't like, it immediately went back to what it was like with the previous setting when I set it back (so it was easy to experiment with). For example, if I set framebuffer uploads to 0 in the OGL2 plugin, the effect was immediate (duplicate cursors) but if I set it back to 1 or 2 it fixed it up without weird effects or having to restart the game.
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Main PC:
Asus P6T Deluxe, Intel Core i7 920 C0 @ 3.7 GHz (195x19, 1.3v core, 1.84v PLL, 1.3625v uncore) w/Thermalright Ultra 120 Extreme, 3x2 GB G Skill PC3-12800 @ 780 MHz, 7-7-7-21-1T, 1.66v; ATi Radeon HD 4870 1 GB @ 790/1000 w/Zalman VF-1000, 300 GB WD VelociRaptor, 4x500 GB WD RE2 (RAID 10), 3ware 9650SE-4LPML RAID controller, SB X-Fi Titanium, Seasonic M12D 750w, CM Stacker 810, Windows 7 Pro 64-bit, Dell 2007WFP
XBL/PSN/WoW: Thordrune