Are there any downsides to installing Lion Server on my laptop rather than Lion?
Actually you have to have Lion to get Lion server which means that the cost is really $30 + $50. Server configures your computer to host wikis and mail server. It really isn't meant for day to day consumer uses. I wouldn't recommend it. 

If you want to try Lion server I recommend installing it in a Virtual Machine (VMWare, Parallels, VirtualBox) and playing with it that way.