Have been using Ubuntu 9.10 since past 2 months and had similar power and screen saver options as I do now after upgrading to 10.04. ( "sleep" after 1 h, "lock screen" after 10 min, "hibernate" when "close lid" on a Dell 600m laptop)
With Karmic, Never had issues with closing the lid while the laptop was sleeping. Three times in a row noticed that if the lid is closed while laptop is in sleep mode, opening the lid results in a blank screen, HDD and CD drive spins, fan turns on. No response to keyboard and/or mouse. Pressing the power key: no response.
The only solution is to shut-down by holding the power key down for a few seconds and reboot.
Cant imagine why there would be a problem, but wondering if there are others who also see the same thing and if there is fix to this. Right now, have disabled sleep and will see if problem shows up.