My $0.02:
Rubicon05, you are right--the aircraft are at a premium. Federally, there is a shortage of air tankers.
Currently, 4 Air National Guard and Reserve units have activated MAFFS-capable C-130's to supplement the tanker supply. Two of those units are operating in Boise, 2 in Sacramento.
Nationally, we are at preparedness level 4, as is Northern California, Nevada, Oregon, and Washington. The Eastern Great Basin (ID, UT, parts of CO and AZ) is at PL5 (critical drawdown). The other regions of the country are at PL2 or PL3. I think given the number of fires nationwide, there is significant competition for the federal tankers.
The lightning events of the past couple days in Northern California have sparked several large fires. New incidents typically get priority over existing fires when assigning air tankers. However, several of the Northern California fires (Chips, Ponderosa) are threatening communities, which means that tankers assigned to these fires can be put in a no-divert status.
As you probably know, air tankers cannot fly indefinitely. Each pilot has a an 8 hour/day limit and a 42 hours/6 days cumulative limit, at the Federal level. CAL FIRE may have further restrictions. So you sometimes hear aircraft "timing-out" due to the pilot reaching a flight time limit.
Currently, Federal and California helicopter drawdowns are at "Critical" levels (less than 1/3 of initial attack helicopters available). Several California Air National Guard Blackhawks are currently seeing use over the fires performing bucket drops.