eslHQ - difference btwn been doing/ done?

There are three basic differences between present perfect simple and continuous forms :

1) When the action is a event starting in the past and continuing to the present moment, the meaning is identical : I've lived here for 10 years = I've been living here for ten years

2) When the action is past but the time reference includes past and present then the difference is between a completed action and an on-going action :
Simple = completed action : I've read "War and Peace" this week (and finished it)
Continuous = on-going action : I've been reading "War and Peace this week. I'm already at page 202.

3) When the meaning is a past action with a present result, then the difference is between a single action and a repeated or ongoing action :
Simple = single action : Oh! I've cut my finger!
Continuous = repeated, ongoing action : Someone has been cutting pictures out of this book.

Your example falls into category 2. Using the simple form would suggest that the speaker wants to know what you've achieved/completed, and could potentially sound accusatory :
Every time I've seen you this week, you've just been sitting at your desk looking at Facebook. What have you actually done this week?

The continuous, on the other hand, sounds more like a general enquiry about what's happening : Hi, what's up? What have you been doing this week? Anything interesting?

I have a strange feeling this question has come up before, so I may be repeating myself here.