ty71803 - Yes and no. The holiday season officially ends on January 2nd in 2011 (though the end date changes every year). That has been the date that has circulated around since July. There is a reason why there is an end date to the season - because the seasonal activities and decorations have to end!
So, while
Disneyland will not be able to remove all of its decor overnight, in the wee hours between Sunday, January 2nd and Monday, January 3rd, they can get a lot of it down in one night. It takes longer to put the stuff up than it does to remove it. You may see the leftover things that the workers are not able to take down yet. There may be some remants of the holidays around, as well as discounted holiday merchandise.
It is quite possible that It's a Small World Holiday may stay open until mid-to-late January, as it did in January of this year. They will shut down Haunted Mansion Holiday as soon as January 2nd passes, and they may not want to shut down IASWH at the same time, leaving two big rides out of comission for a couple of weeks, simultaneously. So you may have a shot at IASWH, but it can't be certain.
I would assume that since the CALIFORNIA letters are coming down forever by January 4th, they will probably leave the candy cane version of them up until then - but only because the letters are coming down forever on 1/4 anyway. Otherwise, the candy cane stripes would be gone after 1/2/11.
Also, there is much more to the holiday season that just the decor. There are many things to do as well. There is the nighttime Winter Castle - that will stop glowing after January 2. There is the snow on Main Street - that will stop falling after January 2nd. Santa will be long gone, as will the strolling carolers. The holiday music that fills DL will stop playing. The Reindeer Round-Up will shut down. Most likely, the holiday fireworks and the Christmas Fantasy Parade will stop after 1/2/11, although it did say on the DLR calendar that the parade would be happening on 1/3/11, which could be a misprint (we're not sure).
So you may see little traces of the holiday season here and there, but it's not going to be the full seasonal array of offerings.