The maximum number of qtrees is 254 (per volume I think).
Yes -- that's exactly right. It's 254 (off-by-one error on my part), and it's per volume.
This value is the natural result of using a 16-bit q-tree ID in each inode.
Don't count your bits before they're hatched, Dave. :-)
Presumably you meant "8-bit q-tree ID in each inode":
uchar tid; /* Tree id (for tree quotas). */
I was just taunting Val...
Dave