I own 3 Acer Inspire ONE's (all with the 120GB HD and XP Home). I use mine almost on a daily basis (it fits so nicely into my briefcase......no more carrying a briefcase and a notebook bag..hehe) and the 2 ONE's my kids are using are seeing a lot of use ranging from wireless internet access (browsing, chatting, etc.) to gaming (my oldest plays games like starcraft etc. on his ONE....I'll have to get him to try SINS on it! 
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I chose the Acer ONE's after considerable research at the time (this was back in July-August.....before the Dell Mini was actually available), however I have had a chance to play around on a DELL since I purchased the ONE's and still find I made the right choice for me going with the Acer.
IMO......the Acer ONE has the most "solid" build feel and for me that's a big plus. The wireless adapter performance (ie. range etc.) also seems better on the ONE as opposed to some of the others (MSI Wind, EEE PC, Mini) I've played around with. The MSI Wind has the best keyboard of any netbook on the market at the moment. The rest of the netbooks all have their own individual keyboard "quirks" (keys being sized much too small, or keys being re-arranged!)....which may not be important to some but I found especially annoying on the Asus EEE PC and the DELL Mini.
The one major drawback to the Acer (again....IMO) is that nothing is really accessible (in terms of opening the thing up etc.) If you ever have to open the Acer for any reason whatsoever, make yourself a cup of coffee and a sandwich and settle in for an adventure.....hehe
The Acer has 2 SD memory slots (one is set up to immediately augment your available storage) this is however a moot point with the ONE's I have as they're already the 120GB hard drive version.
The second not so hot thing about the Acer ONE's is battery life. Unless you spring for the 6-cell battery (which is also a tad heavier/bulkier you won't be getting much more than 2hrs of battery usage out of your ONE while using the wireless and moderate hard drive usage. If you were to keep the wireless disabled, your screen turned down to low (it's still bright enough on low for most occasions) and the hard drive usage to minimal you might squeeze 2.5-3.0 hrs. out of your battery if you're lucky!
I'm sure as time goes on the offerings from all vendors will be eclicpsed by other products but for now....... I love my ONE! 
the Monk
