I have a Lenovo G580 (4GB DDR3, ~500 GB HDD, Intel i3). I installed Ubuntu using the in-Windows installer on my Windows 7. Ubuntu was (and still is) slightly sluggish.
By sluggish I mean, the OS GUI is perfectly responsive, but an App's GUI sometimes just hangs/freezes for a second, while the rest works, but the app itself can't be accessed (happens with Google Chrome mostly, but other applications suffer, too) and it fixes itself after a few seconds.
I recently installed Windows 8 and it appears to be the same.
Another problem I am experiencing is that, when I try to boot it up, from the Windows 8 boot menu, it doesn't work right away. I have to select Ubuntu, and then I need to reboot the laptop (long press the power button on this laptop), which then automatically skips the Windows 8 boot menu and goes to the Ubuntu login screen. Also, it takes a really long while while it loads up and gets to the login screen (at first it's just staring purple/pink for around 20 seconds, and then when the logo and that load indicator appear, it is loading for 2 to 5 minutes).
I really love using linux for development (since I don't have to constantly use git to test it). But, this sluggishness is really getting in the way. 🙁
Best Answer
That's because the Wubi installation of Ubuntu is not "the real thing". Disk IO is much slower.
See the answer to this question
I never understood the appeal of Wubi. Install the OS as an actual OS. Put the .iso on a dvd or flash drive and install it next to your windows install. As it stands now, your Ubuntu is pretty much an app running inside Windows. (I exaggerate a bit here)
Once you've installed Ubuntu properly, you realize that the sluggishness is on the Windows side of things.