I have a question that's bugging me.
Let's say I do a TFP/TFCD shoot with a model. So I'll give her the image files and she'll proudly show them on her Facebook page.
I however submit them, let's say, to Getty with exclusivity.
Does the model (or I) have to fear any legal issues?
How do you guys handle that?

There's a thread on iStock which has raised doubts, but has never been answered by admins.
The start of the thread was this post, dated December 11th. It's been bumped several times with a request for official clarification, which has never been forthcoming.
Note that it is not uncommon for two people asking the same question to Support to get two conflicting answers. Also, some advice from Support (on various other issues) has no backing from the ASA and seems to be 'made up out of their head'.
Notwithstanding that, here's the OP from Dec 11th:

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I just wanted to share with you this information because some time ago there were threads telling that Facebook was OK for exclusives.
My models always ask if they can upload images received from me to Facebok (when the shoot is TFCD).

I also have a personal Facebook profile fan page where I would like to put web-sized versions of my images. I agree Facebook gives a great visibility and it is nice to get potential new contacts/clients this way. I see that many exclusives upload images there, even inspectors and admins. Some exclusives even use the images with the iStock logo (Download a comp) on personal sites and on Facebook.

For a moment I thought - well, if they do it, then it should be ok. Still I wanted to be sure. So I asked support several times about Facebook and showing images on web in general (what size, yes or no for personal and iStock-logo watermarks etc). They told me they had especially consulted iStock's legal team about this. So here is the reply:

As for facebook, when you upload an image, you represent and warrant that you have full rights to the image, and are in a position to grant facebook a perpetual Royalty Free license. So in this respect, your models, or any customer who purchases the file should never be uploading the images to facebook, as they do not have any rights granted to them.

As for photographers, technically you are the copyright holder, and are able to grant these rights, however you are essentially granting facebook redistribution rights without compensation. Watermarked images with the iStockphoto watermark should not appear on facebook or any other live site. Using facebook to advertise your iStockphoto collection is generally not a good idea, because you are giving away rights to your images and opening yourself to misuse or piracy which facebook will not protect you from.

In short, I cannot tell you that it is OK for you to post images to facebook, however if you choose to do so we may or may not take any action. Models or customers however should not be posting any content to facebook.

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Several contributor posts suggest this is not correct, but nothing official has been posted.

Hi ShadySue -

I think below is not accurate - does anyone have definitive answer? If it IS accurate, then I need  to get some pics off FB  

"As for facebook, when you upload an image, you represent and warrant that you have full rights to the image, and are in a position to grant facebook a perpetual Royalty Free license...."