I've looked around and seems like various problems around suspend are wide spreaded for 14.04 release, nevertheless I haven't seen exactly my problem reported, nor my laptop model mentioned.
So, the problem.
When I press sleep button system seems to be going into suspend, i.e. screen goes black, it stops responding on the keyboard and wireless LEDs turn off, however the power LED doesn't go into suspend state and CPU fan also keeps spinning. But unlike the other problem described here https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1315435 when I close the lid and reopen it - system wakes up and goes back to normal locked screen state, so reboot is not needed.
This is a clean freshly installed Ubuntu 14.04, 32bit
Laptop Dell D630