32 GB, IIRC, is the largest size specifically mentioned in the specification; anything proclaiming SDHC compatible must handle up to 32 GB, but there's no guarantee past that.

However, the larger sizes (up to 2 TB) are handled exactly the same way, so unless a device's firmware (in our case, a kernel driver) does something deliberately ******ed, it'll work with them, too. (I haven't read up on the SDHC spec and the kernel code to see if there's such a bomb, but even if there is, you can bet it gets fixed as soon as a big card is on the market...)