What may be confusing in this passage is that the phrase old hat is usually used to describe objects or activities with which one is very familiar. The correct way for this author to use the phrase would have been to write:
Staying on the cutting edge of social media is old hat for 28 year-old Soraya Darabi.
According to the blog Publisher's Round-up, the author made a mistake in this passage and should have used the phrase old hand:
old hand |oʊld hønd|
noun
a person with a lot of experience in something : he was an old hand at red-tape cutting.
(As an added twist, The Phrase Finder, claims the saying old hat may have originally referred to a woman's private parts. I imagine this would have made the above mistake less forgivable to an earlier audience.)
... you can't present perfect (or continuous) and past simple within a sentence.
As it stands, this rule is incorrect. In many cases it is acceptable and logical to mix past and present references in consecutive clauses
I lost my keys last week, but now I have found them.
This makes sense: A was true then, but B is true now.
This, however, does not make sense:
He has decided to go hiking, so I went hiking as well.
This sentence amounts to A was true then, because B is true now. The simple past describes a past event, your going hiking, but what the present perfect describes is not a past event, his decision, but a present state which is the result of a past event--his state of having decided. That present state cannot be the cause of the past event. The cause must be either a past event or a past state:
He decided (event) to go hiking, so I went hiking as well or
He had decided (state) to go hiking, so I went hiking as well.
The important thing is not to mix time references illogically.
As for the sentence in your friend's email:
Getting that email was such a pleasant surprise, because I was just thinking how I've been wanting to send you an email
There is no mixture of time references here, because the progressive construction "I have been wanting" marks a state, not an event, which may very reasonably be taken to continue into the present out of a past which is marked (by "just") as immediate. In effect, these pasts inhabit the same time frame as the present.
In any case, the "rules" are very loosely applied in informal discourse; see my discussion here. A casual email, which your friend probably dashed off in excitement, should not be held to the formal literary standards of coherence.
Best Answer
Both are acceptable grammatically.
In the first, the object clause is written in the imperfect tense (past continuous). In the second it is written in the past tense.
Neither example can possibly imply that the person described as 'you' is still staying at the hotel. But the first could well imply that 'you' were still staying at the hotel at the time 'I went'. But with the 'when you were in New York' clause included, it does not seem possible that I could have gone to the hotel when you were still there.
Edit 4 July 2020. When I wrote this answer nearly six years ago I said "it does not seem possible that I could have gone to the hotel when you were still there". I think that was a mistake. I don't now believe I meant that. It seems perfectly plain that option 1 leaves open the possibility that my visit to the hotel took place while the other person was still there.
It does not matter that the principal verb in the sentence (went) is in the past. The action of 'I went' has nothing whatever to do with the tense applicable in the object clause. One could equally well say: 'I went to the hotel where you will be staying when you are in New York', or 'I will go to the hotel where you were staying...'
I think both sentences mean almost exactly the same thing. The second is perhaps more applicable to a very short stay, where there were also stays at other hotels.
The French would always use the imperfect (imparfait) for this type of thing, but in English you have the choice.