Hi I'm not aware of what may have caused it or it occurring in the past, however I very regularly tether my iPhone 5 3G connection (with Three) to my Macbook over USB. This is because my home broadband never surpasses 4mbps and yet my 3G connection, 90% of the time is 10mbps+, often nearly 20mbps. Anyway, just recently I have noticed the tethering is horrendously slow. If I use the 'Speed Test' app on my iPhone I will get speeds of around 15mbps as expected over 3G, however now when tethering and running the Speed Test website on my Mac I am only getting approx. 2-4mbps. I've hopped back and forth and it getting full speed direct on the iPhone but crippled speeds on my Mac. Why might this be? Hope you can help me resolve this, its a real pain in the ass! Anyone else suffered the same before?