The problem time periods are around Federal holidays (three day weekends), Easter, Thanksgiving, Christmas and New Year's Eve. Also the entire month of December is really popular with
DVC members because of the lower cost of points per night and you can see the holiday decorations and there special events going on too, including:
The Candlelight processional
Mickey's Very Merry Christmas Party
Filming of the Christmas Parade for television broadcast
DVC Merry Mixers
Osborne Lights
And probably other things I've forgotten.
As to each resort:
BCV will be hard to book any time schools are out including spring break. It's also a small resort so the rooms are limited.
BWV and
BCV will be hard to book during Food and Wine--not impossible but hard.
BWV - Standard View are difficult to get at the 7 month mark.
VWL - December -- Christmas week through New Year's Day -- Very hard if not impossible to get unless you own there. This resort is also small so that is another reason it's sometimes hard to get into.
BLT - Theme Park and Standard views during any of the times mentioned above for any of the other resorts is hard to get.
AKV - Concierge, aka Club Level - there are so few rooms that it's really hard to get unless you book at the 11 month mark. Also AKV values fill up early and are difficult to get during busy seasons, but not impossible.
OKW - the Grand Villas are difficult to get at the 7 month mark around the holidays.
SSR for the THVs - the THVs have been very popular. This might change because the 2013
point chart raises the cost to rent a THV but right not many families choose a THV over a 2 BR at SSR.
A lot of the resorts are hard to book at the 7 month mark around the first weekend in January when the Disney Marathon is run.
What many members do is book at our home resort at the 11 month mark and then at the 7 month mark, try to switch to our desired resort. Sometimes we have to do a waitlist.
I'm not familiar with HHI and VB as to their busy times. But I've heard it's hit or miss to get into VGC at the 7 month mark.
My DH and I have been trying out the various DVC resorts for the last few years buy booking our home resort and then switching. We had to WL for a reservation in October 2010 at BWV but it came through within a few days.
Hope you enjoying trying each resort as much as we have. The ability to stay at other DVC resorts is really a nice perk of the DVC.