LinkedIn.com as a personal CRM Tool

I'm using LinkedIn more and more as a personal CRM tool. That is when I meet someone, I send an invite to link with him/her on LinkedIn.

I add the contact details of the received business card in the LinkedIn.com address book.

And in the notes, I write down some details of the contact or the meeting I had.

What are the benefits of doing this?

1. Contact information is always available. (I use LinkedIn also on my mobile.)
2. I don't think there are any storage limitations on LinkedIn contacts.
3. Fast, easy and simple.
4. My outlook address book stays clean.

What could be better...
(I could be wrong about this, so your feedback is welcome!)

1. You have to send an invite before you can add details. So I keep the received business cards until my invite is accepted.
2. I need groups of relations. It would be great if you could indicate that a relation is active or passive. A ranking from e.g. 0 to 9 would be great.
3. The address book functionality of LinkedIn.com is not always stable, so sometimes you have to push the save button several times before your information is saved.
4. Linked to linkedin.com. There are exchange possibilities, but we keep having several address books.

Do you use LinkedIn also as your CRM tool? Do you have extra tips or feedback? Be welcome to add them as comment on this post.