user1760: This is quite a basic question.
Namecoin allows any arbitrary text as data:value pairs. How big can the data be? 100 bytes? 1 MB? I am not sure.

user257: 520 bytes for name_update to work
http://dot-bit.org/forum/viewtopic.php?f=2&t=503
It should be twice that amount but there is some bug.
As you can read in the forum thread some planning is going on to increase it to 9kb. 

1760: <p>This is quite a basic question.</p>

<p>Namecoin allows any arbitrary text as data:value pairs. How big can the data be? 100 bytes? 1 MB? I am not sure.</p>
 257: <p>520 bytes for name_update to work</p>

<p><a href="http://dot-bit.org/forum/viewtopic.php?f=2&amp;t=503" rel="nofollow">http://dot-bit.org/forum/viewtopic.php?f=2&amp;t=503</a></p>

<p>It should be twice that amount but there is some bug.</p>

<p>As you can read in the forum thread some planning is going on to increase it to 9kb. </p>
