Grasses prefer to be split in the spring.

Hm, maybe it's a California thing, but the Sunset book I have said it's best to split them when they recommend planting them and it said fall for that. Probably because our winters are mild and rainy? I was thinking of waiting until spring until I read that too. Oh well, I guess it's pretty hardy and will probably survive whatever I do to it... hopefully... ;)

Yea...it is more of a dormancy thing here...

They sleep pretty heavy over the winter and are in the process of storing food for the winter in the fall (best not to disturb this process).

When the new sprouts emerge in the spring is the best time to dig/divide/transplant in our area.

In general, grasses need to be divided near the beginning of their growing seasons. For warm season grasses, this is after winter, and when the soil starts to get into the 60-70 F range. This is true no matter where you live. Even California has periods of cooler weather and soil temperatures. Warm season grasses need a good bit of time to establish themselves before cooler weather forces them into dormancy.

Cool season grasses have (at least) two distinct growing seasons each year, and can be divided at the beginning of either, with no ill effects. In my coastal climate, I frequently have better luck dividing cool season grasses in the fall. They have a very long time to establish before having to deal with adverse weather. Spring divided grasses have only a couple of months before hot summer weather forces them into dormancy.