Netbooks are all about expectation.
I've had this Dell Mini 9 with 10.5.7 and now 10.6 and I love it, it's exceeded my expectations.
I've pretty much gotten used to the keyboard totally now and type about as fast as I do on my iMac's keyboard (the only exception is using special characters).. hell it only took me maybe a week to get it done.
My only real complaint is the heat, it's fairly hot, about the same level as the iBook G3 its indirectly replacing.. which ran too hot for me.
Also, this is my only mobile computer, and I've used it a decent amount, and the more I do the more I appreciate it. I have to admit it feels snappier in some instances (opening programs, bootup, general responsiveness) then my iMac. The only time the performance has been an issue has been with flash, but I can live with it. I use it for what it's intention was, email, browser, adium, iTunes.. just light use. I'm not editing movies, not expecting HD video, just something thats miles better then using my iPod Touch, just something I can use while I'm in the living room or at lunch.. etc.
I think it's one of my best purchases in recent memory.