From AS Website:
Mileage Plan Redemptive Upgrades
* Requires 15,000 mile redemption for one-way travel within North America and Hawaii
* Redeemed by calling Alaska Airlines Reservations at 1-800-ALASKAAIR (1-800-252-7522)
Mileage Upgrades are booked in "U" Class and can be used in conjunction with Value or Full Flex fare categories only.
Mileage Upgrades exclude free, tax/PFC only, award travel, industry, promotional discount or two-for-one fares. Mileage Upgrades can be used in conjunction with Money & Miles (AS50) Award Tickets. U Class may not be available on all flights. Value and Full flex fare categories are booked in Y, S, B, M, or H classes of service.
Sorry to say
ppcinfo but not only are the fares restricted on what is UG'able, they changed the number of miles required from 10K to 15K one way... This was first announced at the start of Summer 07 (I think) and was invoked on all reservations August 1, and on... (approx)