Very slow login on Ubuntu Karmic

"This is not exactly an answer, but more of a collection of ideas on how to track down your problem. In my experience, these kind of delays happen because of one of the following:

Real need for processing lots of stuff.
Run out of RAM and use of swap-space.
Waiting for a service that either takes time to start, either fails entirely to start (so that the computer waits for the request to time-out).

You could try to investigate more by running on a TTY (ctrl-alt-F2, for example) the programs top (show you CPU usage) to rule out #1 and mem (shows amount of used memory) to rule out #2. Of course you should do this while on the graphical console you start your GUI session.

If it's #3, then you should investigate your logs. You could use bootchart as suggested in furtelwart answer (+1) or looking at the logs directly. All relevant logs in ubuntu are under the /var/log directory. I use Gnome/GDM and my logs are stored under /var/log/gdm. Chances are yours will be under /val/log/lxde.

HTH!"

Check your /etc/hosts and /etc/resolv.conf for invalid localhost entries. Remove them and the problem should fix itself.