One of the major difference that Windows users find while switching to Ubuntu will be the overheating issue. The CPU and Graphic card temperature will almost reach 60 degree celsius even when the laptop is idle. And some users will also find reduced Battery Backup in Ubuntu.
There was a tool known as Jupiter that would save power and also solve overheating issue but the project is closed now.
Here is an alternative to Jupiter known as TLP, which does a great job by switching to battery mode and reducing temperature of CPU and Graphics card. Once you install this tool, you will find a difference of 10 degree celsius in temperature.
To install in Ubuntu, open Terminal
sudo add-apt-repository ppa:linrunner/tlp
sudo apt-get update
sudo apt-get install tlp tlp-rdw
Start TLP in battery mode using this command
sudo tlp bat
In few seconds there will be huge fall in temperature in both CPU and Graphics card.
You can get better results by editing the TLP configuration file.
sudo vi tlp
Remove the # before the word CPU and replace ondemand with powersave
Save the configuration file and restart TLP
sudo /etc/init.d/tlp restart
Switch to Battery mode
sudo tlp bat
This will reduce power consumed by CPU and also reduce temperature at a huge rate.