I wrote about a similar issue recently when I tried to update db4free.net's phpMyAdmin to 188.8.131.52 and couldn't do so because the latest phpMyAdmin versions refer to information_schema instead of SHOW commands. Now there's another problem that shows that queries on information_schema perform much too slow on large servers - I can't execute a simple SELECT * FROM INFORMATION_SCHEMA.TABLES query on db4free.net's MySQL 5.0 server anymore. After running for quite a long time, it fails in a "ERROR 2013 (HY000): Lost connection to MySQL server during query".
I guess that many MySQL DBAs must have similar problems. Now I've filed an official bug report with Severity S1.