Originally Posted by Morrigan

Let's assume you've got around 900 haste rating with a spell stone (27.5%), plus 5% + 3% through raid buffs, then your corruption will tick every 2.176 seconds on a single target.
The duration of the trinket proc is 5 seconds and it has a 20% chance to proc, thus its uptime is around 1 - ( 0.8 ^ ( 5 / 2.176) ) = 0.401, so you are looking at a trinket with a 220 * 0.401 = 88.2 spell power equivalent, maybe a little more during eradication/heroism. That is, in a single target situation, but still... looks pretty crappy.