Storage cards are highly reliable. Most problems are due to external events, like the camera running out of battery power while writing images. I've shot about 35,000 images with digital cameras, and the only images I've ever lost were with a Kodak DC4800 running out of battery before saving an image. I've shot 27,000 frames with a 1Ds and Microdrives with zero card problems. Some of the very cheapest cards may be kind of flaky, but all the major brand names (Lexar, SanDisk, IBM/Hitachi) are very reliable, and have decent warranty service if you do get a lemon.
Microdrives are generally cheaper than flash memory cards, but are more delicate. Treat them like a hard drive (don't drop them on hard surfaces, or squeeze them in the middle of the case) and they will perform reliably for a long time.