Thanks for replying, Hv!

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It would be best to not exceed 2000IU daily.
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Are you talking about 2,000 IU of active D3,

No, supplements do not provide active D₃.  If they state D₃ it is the inactive form.  The active form last time I checked was about $600/kg.  So it is too expensive and manufacturers will go with the inactive form.

so if you took 10,000 IU of inactive D3 and only 2,000 IU of that ends up getting converted into active D3 then it would still be alright?

Yes.

Comparing with the recommendation in the following article, 2,000 IU seems to be very conservative.

http://www.naturalnews.com/027345_Vitamin_D_exposure_sun.html

It says, "Ideally, your blood level [of 25(OH)D as per blood testing] should be around 60-80 ng/ml, as this allows the body to have some vitamin D in reserve, and it duplicates the higher levels found in young, healthy individuals who spend a decent amount of time in a sun-rich environment." (My note added for clarity)

Now, assuming an average of 2,000 IU per 20 ng/ml and doing the math, if your blood test shows that your blood level of 25(OH)D is only 10 ng/ml, then you would need to supplement an additional 5,000 to 7,000 IU in order to get your blood level to the desired 60 to 80 ng/ml range. On the other hand, if your blood test shows a level of 50 ng/ml, then you would need to supplement an additional 1,000 to 3,000 IU to get to the ideal range. What do you think of their recommendation that 60 to 80 ng/ml is the ideal range?

There is a lot of controversy over the higher doses recommended by some sites.  And since vitamin D can build up there is really no reason to megadose to begin with as far as I am concerned.

Furthermore, what they are stating is not taking in to account dietary sources of vitamin D nor what the body will produce from UV exposure.

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How much vitamin D a person will produce is dependent on various factors such as amount of melanin in the skin, amount of skin exposed, amount of UV light in the sunlight and length of exposure. Also keep in mind that the inactive D3 produced still has to be converted in to active D3. Simply getting sun exposure does not guarantee this. The production of vitamin D3 is dependent on a properly functioning liver and in to active D3 by properly functioning kidneys.
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Let's say you stayed out in the sun for 30 minutes and your body was able to produce 5,000 IU of active D3 from all that exposure. Would that be bad since 5,000 IU is way more than 2,000 IU that you consider safe?

The body may or not produce such high levels.  What they find cells will produce in a Petri dish does not mean the same occurs in the body.  Does the body have a feedback mechanism to control its vitamin D production?  We don't know.  

And oral intake of vitamin D is not the same as vitamin D produced by the body since oral vitamin D intake can significantly increase the absorption of calcium and phosphorus from the gut, which are some of the dangers some researchers are worried about.  Vitamin D produced by the body and being used elsewhere is not posing this problem.  So in a way you are trying to compare apples and oranges.  Therefore, until I see some real evidence that high oral doses of vitamin D is safe I will stick to the conservative side.  But more and more research is coming out showing that there are possible risks from high oral doses of vitamin D.

I would find it hard to grasp that only 30 minutes of sun exposure could be bad. Am I missing something?

See above.

Is active D3 produced from sun exposure safer than active D3 produced from supplements, so you can safely have much more of the former than of the latter?

I would say yes for the reason explained above. Not all vitamin D produced from sun exposure is used to aid the absorption of calcium or phosphorus, both of which can be dangerous in high doses.  Yet oral ingestion of vitamin D supplements will significantly increase the absorption of calcium and phosphorus.