I'm experiencing the same problem in Win7 with 1.8, I haven't open the client for a few weeks but now it doesn't open with my "wallet.dat" file as argument, if I don't use my wallet.dat then the client opens normally asking to create a new wallet.
I couldn't figure out any trace of the error, the application simply appears and disappears in the win task manager.
Luckily I had a copy of the previous version and that one opens without any problem my existing wallet.
Move your electrum.dat file and restore from seed on the 1.8 client when prompt
Indeed, the seed restoration worked in the latest version ( 1.8 ) but of course I've lost all the customizations/notes of the original wallet

We probably need to make more regression tests between versions so upgrades don't break existing client data.
Thanks for the help.