After 6 weeks with Ubuntu 8.10, aka Intrepid Ibex, the change that has most affected the way I use my laptop is the new network manager. Connecting to a wireless network is easy and just works. It is generally fast to connect, definitely faster than with 8.04 aka Hardy Heron. It will immediately recognise networks it knows about and connect automatically. In particular, it is much better than Windows at connecting to a Wi-Fi network that does not advertise its SSID and recognising it later as a known network.
But the biggest benefit is the support for 3G modems out of the box, in particular the Huawei models available in the UK. When I plugged in my 3 USB modem for the first time, it recognised the device, asked me what country and what operator I was on and that was all the configuration I had to go through: no software to install, instantly on. It also integrates seamlessly into the network manager so there's no flaky third party software to use every time I want to connect. I just have to plug the modem in, select it in the network manager drop down and hey presto, in a few seconds I am online, whether in a pub, on the train or anywhere I've got network coverage from 3 (which is sometimes a bit patchy, I have to admit). OK, there's one thing it doesn't do, which the Windows version does: it doesn't tell me how much of my monthly quota I've consumed. However, I very rarely download large files via the modem so I've never reached the limit: large files is what the (fast) home broadband is for. It would be more important for someone who does use a 3G modem more heavily than I do. Maybe that's a feature to ask for in the next version?