I too find it's hard to find interesting places to eat in the Creek or Lafayette. We have found a few though. Just went to brunch the other weekend at Artisan Bistro. The food and service were great, I'd like to go back and try dinner there. The atmosphere is not really "fun" but definitely upscale and relaxed, looks like you're in someone's house. If you like sushi be sure to go to Kane (there are locations in Lafayette and Danville) the sushi is fantastic! The service can be iffy, but everyone's super nice, I think they get too busy for their own good. You can also go to the Lafayette Chow outpost, I guess it's technically in a mall-ish type area, but always a crowd pleaser. In Walnut Creek, I've heard great things about Va di Vi, but have yet to try it. For fun you might like Havana, the mojitos are a bit of a rip-off but the cuban sandwich is killer.
Hi there, sorry I don't have any specific Walnut Creek recos, but I would like to recommend following the D Blog in the food and wine section on the Diablo Mag website. Lots of great tips in there, and I see good 925 places mentioned. Here's the home page for the f+w section: http://www.diablomag.com/Diablo-Magazine/Food-Drink/