If for some reason you've been living under a rock, RuneScape is having an experience bonus weekend starting March 12 to March 15, 2010. This announcement came out-of-the-blue on Friday via a developer blog.
The two top skills contending for this update are herblore and summoning. People are stockpiling already and prices are skyrocketing. For those trying to buy any secondaries/tertiaries for current training are discovering themselves locked out of supplies. Big money can be made from this and I expect the highest prices will be a day or two before and the start of the event. This is affecting the rares market as a few people are willing to trade santas and Halloween masks for ingredients.
Skills that put you in contention with other players for resources will likely be crowded, such as hunter, slayer, mining and the combat skills (attack, strength, defense, range). Expect to do much world hopping to find semi-open training spots.
Alternative to fighting for resources is training where a crowd is either helpful or non-hindering. Runecraft via the abyss on W36 and become part of the herd against revenant attacks. Run laps on the agility course of your choice. Farm trees and herbs; planting trees the day before and checking the health on Friday may be sneaky but well within the rules. Bury every bone you find since house altars and the Ectofuntus don't count.