Paid .... Now what ????

Hi WPMU - so I've been a free member for a long time, and after getting good email support this week I decided to take the plunge and pay for an annual subscription.

So - I've paid my money ...... now what ??
I thought the API key provided to me by WPMU was something that I would be able to plug in to my client sites, then when I was on the client instance of WP, I would be able to download and install the plugins provided by WPMU, and all the updates would be pushed out to their site as well.

So ....... I'm not sure what to do now.
The plugin that initially interested me was the Fundraising plugin. But - I did not have to pay for that under GNU did I ? So - if I didn't have to pay for the plugins provided to me by WPMU, why did I pay the fee ?

Please enlighten me!!!

It's freakin weird too - I've been a web dev for 15 years, so it's not like I'm a noob.

THANKS (for what I'm not sure) lol