<p>Is it possible to add comments somehow, somewhere?  </p>

<p>I don't pretend to be any sort of expert when using MySQL and certainly don't spend all day in it.  More often than I would like I forget how I intend to use a column (usally the bit ones) and would be very excited if I could add a comment to remind me if 1 is good or bad, for example.  </p>

<p>I'd be happy if it only showed up in something like 'show create table', but any obscure place within the table structures would be better and easier to find than the current post-it notes on my desk.</p>

Are you sure you're not looking to use an ENUM column instead? Good MySQL tables should be self-documenting.
An alternate approach would be to comment the schema files that have the SQL you use to define your tables (I assume you have those, and that you're not using PHPMyAdmin to grow table schemas on the fly...)
But if you insist, the
INFORMATION_SCHEMA COLUMNS
table, specifically the COLUMN_COMMENT column, is probably what you're looking for. It's proprietary MySQL syntax though, so I would tend to avoid it (although the idea of database interoperability is really a joke).