- When I sit in front of the TV with my family, for checking a little email or do a little web surfing, it is perfectly enough and I can put it aside easier simply because needs less space and if it has enough battery power, you either don't need the cable having around all the time even if it is kept in reach for a few hours.
- I have a customer where employees walk around with mobile phones for entering data on the street. The data typing could be done more efficiently on a netbook than on a mobile phone if they sit in the car or have somehow something to put it down (wall, table, knee, ...).
- Many IT admins need to be available quite all the time in case of emergencies. I have heard of some doing SSH over the mobile phone in such emergency cases when they are on the way - and they don't want to always carry a notebook with them. If you are a server admin only a mobile phone might be sufficient but I am doing also client support and it sounds just crazy to me doing end-user-support through the mobile phone. I am used to carry a small bag with me (to avoid having the wallet, keys and the like in different small pockets where they either could be stolen easier) which I also do recommend to others and with only a little bigger bag the netbook already fits in there.
- There are a lot of branches where salesmen found it exaggerated to carry a notebook with them. However, looking up customer or product data through the phone is frickle work IMHO. A netbook fits there well I would say.
- When I go to meetings outside the office (e.g. in hotels or restaurants) a netbook is more handy than a big notebook and in those cases I usually just need to take a few notes, do a little surfing or email.
- Despite all the features that are put into smartphones these days, I hardly think, they will get a full features PC soon. PGP plugins for email, Password managers like keepassx, serious word processors and many other things I use on my normal notebook are missing. On a netbook I can use all these as usual - it's just the screen that is smaller (but still bigger than on every smart phone).
- After ripping DVDs to disk a netbook can also be used as a mobile DVD player.
For a long time I could not see a sense in netbooks. I am a developer and hence write a lot of code and a lot of documentation. The screen of a netbook seemed too small at all and keyboards too. But there are a few cases when it makes really sense to carry a netbook instead of a full notebook (that is heavier, and occupies more space on the table), for example: