My first though was "Wow, they are are in beta". I think it might be a little too early to be giving out beta invites, but I suppose that they need some real live traffic to test stuff with.
There's lots that is broken, but there's a couple of neat things as well.
For starters, you create an account and you have your own homepage thing like most other sites. Your page shows the podcasts that you've subscribed to and the episodes for each. There's an RSS feed coming off the page that shows promise, but it doesn't work at the moment.
To find podcasts you can search for them, of course, but there's also a tag cloud that you can use to find podcasts of a specific genre. Again, the tag cloud is broken at the moment - all it has are tags starting with As and Bs, but I can see the potential.
One thing that I really liked was the speed. When I clicked on a podcast to play it, it started playing almost immediately. Nicely done.
I had hoped to write a mini review on Pluggd today, but it's simply not far enough along to get a grip on. Suffice it to say that I'll keep you posted as it evolves.