Netbooks aren't the fastest computers, but they can be useful -- as long as they're usable. If you want your netbook to work and feel like a real computer rather than a toy, I can't recommend Lubuntu enough -- it makes my netbook feel like a whole new machine.
I bought my netbook hoping it would be the perfect portable companion for those quick jobs when I'm out and about -- like updating one of my posts, or touching base with my boss without using my phone. The problem is, those "quick" jobs seemed to take ages on the netbook. Starting up Firefox in Windows seemed to take forever, and forget about opening multiple tabs. Even on Ubuntu, everything moved a little more sluggish than I'd like. Sure, netbooks are always going to be a little bit slower, but when they move at the speed of molasses, it seems to defeat the entire purpose of having one.
The LXDE desktop environment -- the environment behind the Lubuntu variant of Ubuntu -- aims to be a lightweight desktop that keeps low-resource computers running snappily. It still isn't as fast as your uber-powerful desktop or laptop may be, but you don't feel like every action takes five minutes to complete. Everything opens very quickly, and it doesn't waste time or resources with flashy eye candy -- though it doesn't look ugly at all.
A Fast, Full Desktop On Your Netbook
While things like Joli OS and Chrome OS are often pushed as ideal netbook OSes, they never act the way I want them to. In the end, I don't want to use my netbook like I use a tablet or like I use a browser -- I want it to be a very small computer on which I can actually get things done when I need to. Lubuntu comes with a netbook interface, but I'd personally skip it. The desktop interface is super easy to use, familiar and just as fast. Plus, it's Ubuntu -- which means you can install all your favourite Linux apps using Synaptic or apt-get in the Terminal, just like you normally would. If you're at all familiar with Ubuntu, you'll pick up Lubuntu in no time.
Some might argue that an even lighter weight distribution, like the do-it-yourself Arch, would be even better. If you want to go through the hassle of installing Arch with the LXDE environment on your netbook, you absolutely can, but I personally don't want to waste that much time on my netbook -- my secondary or tertiary machine -- which is why I found Lubuntu so perfect. Install it, grab the one or two programs you need to use on it and you're mostly done. You've got a full, usable, desktop OS on your netbook that won't suck up resources.
A Few Tweaks You May Have to Make
Lubuntu isn't perfect -- it is Linux, after all -- so there are a few things I've noticed that you might have do a bit differently. These won't apply to everyone, but they're just a few things I've noticed that you might want to be aware of.
Its Preferences are quite sparse: Unlike Ubuntu, which has a load of preferences in the GUI, Lubuntu is a bit more toned down. Luckily, you probably aren't customising your netbook as heavily as you would a desktop machine, but there are still a few small things you might have to work harder at. For example, I like to swap my Ctrl and Alt keys, which is a one-click process in Ubuntu. In Lubuntu, however, I actually had to install and configure Xmodmap instead. Obviously most of you don't remap your keys, but you get the idea -- lots of preferences aren't available in the GUI, so you might have to set up one or two of your custom tweaks in a more manual fashion.
Windows-formatted flash drives won't mount themselves: For some reason, if you're using a flash drive formatted as NTFS or FAT, it won't automatically mount in the file manager's sidebar. EXT drives seem to automount fine, but unless you use Linux on all your machines, this doesn't help. I haven't found an actual fix for this, but you can always mount the drive manually through the terminal:
sudo mount -t ntfs-3g /dev/sdb1 /mnt/Flashdrive
for NTFS drives or
sudo mount -t vfat -o umask=000 /dev/sdb1 /mnt/Flashdrive
for FAT32 drives. You'll need to also run
mkdir /mnt/Flashdrive the first time you do this. Obviously, you can change
Flashdrive to whatever you want, and you'll have to make sure
/dev/sdb1 is where your flash drive is located (which you can check using Gparted or by running
fdisk -l in a terminal). Just remember to run
umount /mnt/Flashdrive when you're done using the drive to eject it.
Some GNOME-based apps are quirky: Dropbox is one of the big issues here, which is built for GNOME and not LXDE. You should be able to install it as normal, but a few of the GNOME-specific functions -- like opening the Dropbox folder from the system tray -- won't work, but the basic functionality still does. Similarly, MPlayer doesn't seem to disable LXDE's screensaver when you watch videos, which can get obnoxious. Luckily, VLC fixes this problem.
These are just a few things you might want to keep an eye out for. Lubuntu is still pretty young, so it has its idiosyncrasies, but enough people use it that there's usually a pretty simple fix for any quirks you encounter. The overall experience of the OS is well worth it.
Your mileage may vary when it comes to making the necessary tweaks, since everyone needs something different, but overall I've found that even with those, it's been a godsend. It's the first thing I've tried that's made my netbook actually usable for me—I get a full desktop OS without sacrificing much. Of course, your opinion may differ, so if you've found an OS that better suits your netbook, let us know in the comments.