Mechwarrior Online Open Beta starts today, the core game is functional and tons of fun - though keep in mind its still a very early Version of what the game will become!

Here is a link to one helpfull Video that gives an overview about the current game and how it works:
http://www.youtube.com/watch?feature=player_embedded&v=eBe-hoAlIm4
If you get bored from the Mech Variants skipp them and jump to 14:10 in the Video.

List of Weapons, Hardpoints, etc. very well done:
http://mwomercs.com/forums/topic/27065-ohms-quick-reference-sheets-for-all-mech-hardpoints-weapons-engines-pilot-lab-images-pdfs-excel-inside/

There will be more Updates, Tutorials and Hints on the Mechwarrior Online Homepage coming soon after the sites Open Beta overhaul:
http://mwomercs.com/

Also see NGNG for the Weekly Podcast with Insider-Infos, find people to team with at their TS3-Server and get a good laugh about their comic strips:
http://nogutsnogalaxy.net/

MWO is a Diamond that needs still some polish and shaping but dont mistake it for a Stone.
Simply play it for what it is - a tactical combat action sim with giant bipedal tanks based on a fully developed background universe with immense amounts of lore - be part and witness it grow, get polished and shaped over time and let your voice be heard by the Devs to make it the best game ever.

Have Fun!