I also have problems, but that seems to be due to some mess up after purchasing the support subscription.
Here's a snippet from the e-mail I got (notice the empty list of users that have been granted access):
Thank you very much for your order! Here is your subscription information:
* Ext Standard Support Subscription (single developer, includes 40 x-credits)
* Support Key: ************
* Purchase Date: March 28, 2011
* Expiration Date: March 28, 2012
The following sencha.com users have been granted access to the Ext Premium Support Forums:
You have also been granted read-only access to the Ext JS SVN repository:
I used the contact form last week and this morning have sent an email to firstname.lastname@example.org, but no reply so far.