Character limit of field machine name? Is the machine name of a Drupal 7 field limited to 32 characters (including field_)? When I'm creating a new field, the UI seems to cut me off there, but I wonder if this can be circumvented. 

I'm using prefixes to map certain fields to others, and the fact that my prefixed fields are getting cut off is going to make my matching logic slightly more complex.
Yes the length of the field name is hard-coded to 32 characters. It's most likely because the maximum length for a table name in MySQL is 64 characters, and the field API creates tables with names like field_revision_field_name. I imagine the core developers were erring on the side of caution.

It looks like you could squeeze an extra 17 characters out of the field name (64 - 32 - len('field_revision_')), but to do that you'll need to alter the field_config and field_config_instance tables in the database to increase the length of the field_name column (I guess to 49 characters).

I would imagine you'll also need to hook into the field UI forms to increase the #maxlength of appropriate text fields.

It might be easier to re-think your matching logic :)