When would a write through cache be more trouble than it's worth?

We've been talking a lot about using a write-through cache for this new thing we're building. It's nice because it makes sure the cache and the database always match up, and it's easier to keep everything fresh. So, if we need data to be super consistent and read really fast a lot, it seems like the obvious choice. But, I'm kinda worried it'll slow down our writes and make things too complicated if we're writing much more than we're reading. Does it get to a point where the good stuff about write-through caching just isn't worth all the extra work and slower write times? What have you all seen when you've used it?