The same here. my experience is, that with mountain lion the write and read speed of sd cards is way too slow... i have a iMac (mid 2011) an a MBP and both are very slow. Disk Speed test from Blackmagic shows 4.8MB/s write and 18.9MB/s read speed. the card is a class 6 (30MB/s).
Same here, very sad. I paid 70 $ for a 45/90-Panasonic SD and nearly 100 $ for a 95/95-SanDisk SD, both 32 GB. If I'd know this before, I would have bought 2x 64 GB with lower speed for less money.