While I have personally had positive experiences with Lightspeed point of sale, I have been made aware of some stores who have had negative experiences with Lightspeed.
The main issue appears to be related to the multi-location version of Lightspeed not correctly handling the inventory at all locations (ie: transferring the wrong item to the wrong store or the different store inventory databases not syncing correctly which causes on hand counts to be incorrect).
That is all that was communicated to me so I don't know if the problem lies with the user or with Lightspeed but the situation was bad enough that at least one store stopped using Lightspeed and switched to another point of sale system.
I'd advise anyone looking at Lightspeed to do a little research and be sure to talk to stores using Lightspeed to see if they have experienced any issues.
Are you in the US and in need of no cost retail point of sale advice? I'm happy to help and can be reached on my cell at 208-340-5632 (I am on Mountain Time) or via email at firstname.lastname@example.org. There is also a contact form to the right that can be used to reach me.