Ok memcards = safe
save states = usually ok.
The reason that save states get corrupted is because you eithier quit the game to quickly or you save them to quickly or to much data is changing while the state is saving. Good idea to save them twice about 20 seconds apart. If one gets messed up however it cannot mess up your memcard saves. Secondly Yes if they don't save all the data graphical errors can occur. Also don't save during transition points in games... a.k.a. logo transitions like intro. Just don't rely on save states alone to get you through a game.
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Q6600 Core 2 Quad || Soundblaster X-Fi Extreme HD || e-VGA 8800GTX || 4096mb 4-4-4-12-2T Dual-Channel RAM || MSI P6N Diamond || 2x 320GB Hardrive || 5.1 Speakers || Remote control || 8x USB 2.0 || DVD/CD ±RW Drive || 1x IEEE1394