Disclaimer: I'm making the following comments based on my semi-informed knowledge of IP packets and personal opinions based on informed gleamed from Microsoft information. I haven't had practical experience in application of these principles on a Windows machine. I'm just doing my research before "trying" things. Also, excuse the nerdiness below.

With that said.....

The TCPAckFrequency actually does have some merit (I only responded to the QoS change in my last post). Windows attempts to wait for two packets to arrive (set in the registry) before sending an ACK response to the sender. It has the purpose of trying to reduce the amount of work that needs to be done, and reduce bandwidth consumption. The issue is that the wait for the second packet is allowed up to 200ms, by default, before Windows goes ahead and sends the ACK response, which causes latency. The occurance of this kind of delay should be pretty low though, so these 200ms delays should not be occurring very frequently.

So its a bandwidth vs. latency balancing act. Reducing the TCPAckFrequency to a value of 1 should reduce latency, but result in increased outgoing (upload) packets. ACK packets are fairly small, though, relatively speaking. Because you're now delving into incoming packet frequency as a basis of possible response tweaks, results are going to be highly dependent on your ISP network connection to the source. Layman's terms: results will vary, you could have a significant boost, or little affect at all. For most people, you're likely to see a boost to gaming (personal opinion).

Given that upload speeds on most connections tend to be much lower than download speeds, you are increasing load on the weaker part of your internet connection. So keep that in mind. Again, for most people, you probably are not taxing your upload capacity unless you're hosting torrents or something in the background, which is just silly to do in the first place.

As Caspian pointed out, I would at the very least backup the registry before making any changes. The value change to just TCPAckFrequency from 2 to 1 should be rather safe to make, as it doesn't change the ACK response at all, just sends more of them, at worst only affecting your network connection and not system performance. I may give this a shot and monitor network performance. I'm interested in the effect on increased [upload] bandwidth I hypothesize that I should see. I would expect it to be fairly small, if so, but that's just a guesstimation on my part.

Don't suppose anyone else has practical experience in this kind of area?

EDIT: Did just search the other threads on here (sorry, my bad!). Sounds like the ElitistJerks comments about this basically backs up my understanding of the changes. I'll stop posting here about this.