My rule of thumb is to go part time at the job I'm leaving just in case the grass isn't all that greener at the new gig, like @Kompa suggested. This can be tricky because if you're going retail->retail the two companies might see each other as competitors and refuse to hire you unless you quit first. I put in an app at a local chain hoping to pick up some extra pocket money, Target HR said it was fine, but when they called me to set up an interview I mentioned my plans to work at both places and they said NOPE. Lame. It's not like I've ever been privy to any valuable trade secrets at any job I've had so I never understood why the whole "competitor" thing is such a problem. Oh well
I think I'd miss it to be honest...BUT I think my personal life would take a GAIN. I tend to think about work all the time while at home and cant seem to get my mind clear sometimes. Maybe it's because 8hrs isnt enough time to do what I need...hell time itself isnt enough time to do what needs to be done lol