user2075: Are there any services/agencies running a large number of nodes so that they can guess the IP address of a transaction's origin? 
I guess they would need to run tens of thousands of nodes. However it'll be useful in tracing stolen coins. Surely there must be some. 
I have seen talks and papers claiming to do so but not found any such service.

user75001: I see this as a non-issue. By using Tor the IP address of the originator is sufficiently obfuscated.
See my two other posts for some discussion and related resources:
How can I setup Bitcoin to be anonymous with Tor?
What are main advantages of Bitcoin over Monero?

2075: <p>Are there any services/agencies running a large number of nodes so that they can guess the IP address of a transaction's origin? </p>

<p>I guess they would need to run tens of thousands of nodes. However it'll be useful in tracing stolen coins. Surely there must be some. </p>

<p>I have seen talks and papers claiming to do so but not found any such service.</p>
 75001: <p>I see this as a non-issue. By <a href="https://bitcoin.stackexchange.com/questions/70069/how-can-i-setup-bitcoin-to-be-anonymous-with-tor">using Tor</a> the IP address of the originator is sufficiently obfuscated.</p>

<p>See my two other posts for some discussion and related resources:</p>

<p><a href="https://bitcoin.stackexchange.com/q/70069/75001">How can I setup Bitcoin to be anonymous with Tor?</a></p>

<p><a href="https://bitcoin.stackexchange.com/q/72518/75001">What are main advantages of Bitcoin over Monero?</a></p>
