I hear both 残念ながら and 残念なことに when expressing that something was unfortunate before the actual sentence, much like the English "Unfortunately, ...".
However, I'm not sure on where these two phrases differ. Is their usage the same?
I believe the difference is:
These two examples are subtley different. In the in the first case, you are being told that a breakup will happen, despite the fact the speaker is sad about it. In the second case, you are being given a fact which is itself a cause of disappointment.
Hope that helps.
To me, the two are nigh identical. With
According to this site:
Which I roughly interpret as 「〜ことに」giving more surprise/contradiction (but I must admit I'm not all that clear and could be wholly mistranslating that one... anybody care to confirm/infirm?).
At any rate, grammar is slightly different:
I agree with Dave that the two seem very close. If we look at the core definitions, we can see this:
〜ながら: "while 〜"
Although we usually stick this on the end of the verb stem (食べながら、見ながら、など), it can retain the same meaning in English here.
(emotion/feeling word) + ことに(は): "Very 〜", "To my 〜"