Let me repeat the title - be very careful while you use
tasksel on Ubuntu (or a Debian based Linux distribution for that matter).
Here is something that I am going through right as I write this entry that might save you the trouble. I was back from work, and it was 2 AM in the morning but I still wanted to do some setups on my laptop. It had been recently upgraded to Ubuntu 9.10 (Karmic Koala) and I wanted to setup a LAMP stack.
tasksel and saw that Ubuntu Desktop was highlighted. I unchecked it, checked LAMP server and hit OK.
And all hell broke loose.
It was uninstalling the Ubuntu Desktop packages right in front of my eyes!
Well, I killed the process half way through but some harm was done. If I shutdown my laptop now, or it crashes I need to use a CD to recover it. But since I had been through a similar situation before, I know I should be able to recover from this.
It might sound cocky since I am still on the recovery process, but I do have confidence that it will pull through.
Bottom line though is that be careful of the GUI wrappers like tasksel or even Synaptic Package Managers. They can do a lot of harm for the "ease of use" they provide. Stick to explicit command line that does only what is told. And also, do not do critical system changes with sleepy eyes. :)