Well it's been over three days since I fitted the I-Plate to my phone socket and I thought I'd give you all an update. Before fitting the I-Plate I did a number of tests of the speed of my broadband using the Broadband Speed Checker (I did try embedding the speed checker in this post but for some reason it wouldn't work even when I followed the instructions, ah well worth a try). Whilst the numbers varied a bit they were always around the 5200 Kbps mark. Adding the I-Plate didn't seem to make any difference although the instructions did say that it might take 48 hours before any improvement.
So I've just tested it again and I'm now getting around 6200 Kbps -- an improvement of 1 Mbps! Given that I'm on an "up to" 8Mbps service and was told by BT that the most my line would actually support was 6Mbps I'm quite impressed. Added to the speed improvement the broadband has been very reliable since I added the I-Plate -- no slow downs requiring me to re-boot the router and no disconnections. All-in-all I'm extremely impressed by such a small piece of kit that only cost me £1.20!