Graphics & Sound
Keep it simple! Do I need to play games? No. Do I need to decode 720p video? No. Do I need to decode 1080p video? Definitely not! All I really need is something that'll ouput to an external screen at 1,920 x 1,200 or less, while making sure everything displays smoothly and without fuss.
As for sound, the Eee PCs have led the way here with some very good integrated speakers. This is great but if some money can be saved here to spend on something more important, so be it!
While we've seen plenty of netbooks with mechanical drives, I'm pretty adamant that solid state storage, generally in the form of flash memory as opposed to an actual SSD, is the netbook ideal. Though some might lament the limited capacity, the lack of moving parts and minimal heat produced by flash memory means better battery life and cooler running - two fundamentals for any ultra-portable laptop. Moreover, solid state memory takes up less space, so helps keep the chassis as small, light and portable as possible.
How much do you need? Well, I found the 20GB found in the Linux version of the Eee PC 901 to be more than sufficient, but I'd go further and say that internally 16GB is all you really need. This is more than enough for an operating system, all relevant programs and plenty of files and odds and sods. I'd then take an innovation used on the Acer Aspire One, adding a dedicated SDHC card reader that merges seamlessly with the internal memory. This, combined with a USB external drive and a regular multi-card reader, should ensure plenty of flexibility.
Connections & Networking
For the most part there's very little I'd add to most netbooks when it comes to connections. Three USB ports, VGA, Ethernet, headphone and microphone jacks and a memory card reader are pretty sufficient for the usage. My only other desire would be for HDMI, since it makes playing video on a TV that bit easier.
As for networking, despite Apple's best efforts you still need wired Ethernet - so that's a given. For Wi-Fi I'd happily settle for 802.11b/g instead of Wireless-N if it meant saving a few bob, though if I were offered N I'd happily take that, too. Bluetooth, however, is an absolute must. There was something else, too, but I can't quite remember what it was just now…