CF gets slower with use?

[munfai]

I've been using my 512Mb Sandisk Ultra for 2 months already. Transfer speeds now as compared to when I got it is like 2-3 times slower, using the same card reader. Formatting of the card is always done in-camera.

Write speed seems ok, but then again I don't usually take my time between shutter releases.

Any insights on why this is happening?