Scotch-Brite has created the best product for keeping grout clean that I have come across. These grout scrubbers are comfortable and easy to use. There is no hassle of having to rinse out a sponge every few minutes or trying to maneuver the rough edge of a sponge into the grouted areas.

The blue part of the scrubber is all just for gripping, the white part does the cleaning. You can't really get into corners well, so you will most likely need to still use another method for that, but as for grout-lines it works great. You can also use it on other surfaces or areas that have grooves or lines. I've even just used it in a circular motion on areas of the shower stal that had some hardwater buildup and it scrubbed it right off. Just keep in mind that the only part of the "scrubber" that cleans is the white strip - so it is not something you'd clean the whole bath and tub with since you can't cover much area at a time.

Overall I like it for it's specific purpose and a few random other uses - I have also used it to clean some old buildup gunk in wood grooves on a whim.