I have just installed Lightroom5.
First it starts automatically on system switch-on even though it's not in the start-up menu.
Second. It eats CPU and memory. I was exporting 1 picture and memory usage went from 2.4 Gb to 3.6Gb. Cpu 100%
Check in your LR Preferences- General tab > Import Options > "Show import dialog when a memory card is detected"
If this is ticked, then its possible that any device plugged into a USB socket will start LR. Remove the check to try as a first step.
I am not qualified to comment on CPU usage.
Thanks for that. I leave the (empty) card reader in a USB socket by default so easy to sort that problem out!