We went last Jan for the first time ever over MLK weekend - LOVED it and wish our DS's school sched. worked out where we could go every year but didn't work out for this next January. Anyway, I know there is a marathon there in January - might be around the dates you mentioned...so you might have some crowds from that.
Last year I watched the weather online on accuweather.com and weather.com the whole week before but it didn't really help me plan that much. The week before we went I think it was like in the 80's for a couple of days..but then some big 'ole cold front dropped down from Canada and covered like the whole US...our weather really fluctuated during the daytime from 70's down to 50's and back up again over the 3 days. It was still GREAT tho as it was like 20 degrees up here in the north - so regardless you WILL be warmer down there!! We DID go to the pool one afternoon when it got up to like 70 (and we were in Florida so it was like we HAD to!

) but we actually mostly stayed in the hot tub.
I suggest packing layers! I got all 3 of us in one large 15x15x30" duffle which weighed EXACTLY 50 Lbs and 1 carry-on suitcase!!

I made one 15" high stack for each of us and if I couldn't close the bag then something came out! This also helped prevented us from spending a lot of extra money on any souvies 'cuz there was nowhere to pack them!
We wore jeans down which I figured we could wear more than once. It was freezing up here so we wore our ski coats with removable hoods and zip out linings so we had some options (and yes, we needed the hoods one windy day - we had taken the linings out but we got cold without them once the wind picked up). One night we had thunderstorms with pouring rain and LOTS of lightening...we got wet & cold and called it a day early and went back to VWL to get a hot shower and wander around the lodge looking for Hidden Mickeys.
I packed 1 bathing suit each & flip flops for the pool, a pr. of shorts & a pr. of crops for myself and a couple pair of those zip off convertible pants for both DS and DH - those were
really handy 'cuz the mornings & evenings were cool but a couple of the days were pretty nice. I also packed a couple of T-shirts and sweatshirts each, and 1 spare pair of shoes (thank goodness 'cuz our one pair got so-o wet in that storm).
Since we were there over a holiday weekend we had some crowds...it wasn't PACKED but it wasn't empty either - reminded me of late, late summer...there were a lot of those loud, obnoxious Brazilian Tour Groups. But we still LOVED our quick little get-a-way. I am anxious to see DS's school schedule for 2010 already to see if we can plan another January trip (our school system has a "Professional Day" in January and last year they had it on the Tues following MLK so we could have 4 nights w/o him missing any school)! With the price of airfare these days we feel like we need to at least go for 4 nights.
It just felt really cool that Friday when someone at work said "what are you doing this weekend" I loved saying "We're going to Disney"!
