The standard maximum length for user names is 25 characters. If your users really pick up such long nicknames, they may break your blocks' layout, depending on your theme and resolution. This is
because they may appear as authors of news articles etc. in headlines that appear in various blocks.
To prevent your users from using long user names, you must change the maximum allowed length in modules/Your_Account/index.php, in the function userCheck(). Find the line:
if (strlen($username) > 25) $stop = "<center>"._NICK2LONG."</center>";
and change the 25 to a lower length. A better programming style would be to define a constant for this and do the check against the constant.