Experiencing recast bug intermittently as well. Trying some troubleshooting steps for reliable reproduction, and will report back if anything sticks.

ISP: Time Warner Cable
Type of Internet Connection: Cable
Internet Connection Speed: ~8mbit down, ~1mbit up
Date & Time: 12/21/2011 - ~5:45 PM
Frequency: About 50% of the time at the moment. I experience the bug when I first start the game, but it's gone if I close the client entirely and re-open it. Again, troubleshooting to try to narrow this down.
Character Name: Spiriel Sylph
Race: Miqo'te
World: Besaid
Class/Skill Rank: GLA 35 at the time, but the bug isn't job specific
Area and Coordinates: Uhh...Mun'tuy Cellars and Humblehearth?
Party or Solo: Solo
NPC Name: -none-
Monster Name: Any
In-Game Time: Don't have an answer for you, here.
Steps:
1. Turn on computer for the day
2. Open Steam (attempting to determine if Steam is a culprit, unable to duplicate today)
3. Open FFXIV via Steam
4. Use ability
5. Note that recast is shortened by an interval. Usually around 10-15 seconds, today it was 4.
6. Close client entirely
7. Re-open client via Steam
8. Fixed

Notes:
Windows 7 Home, 64-bit
Restarted via OS, unable to duplicate
Full shutdown, wait 20 count, start PC, unable to duplicate
1 synth, change jobs multiple times, mount and dismount, return to GLA, unable to duplicate

May be related to crafting, crafting leves, or using Return somehow. I usually log in, do my crafting leves in town, go deliver my leves at camps, return, then do combat leves. That might explain why it's always the first time and never afterwards.

Sorry, I know this bug has been reported before, and I realize it's a bear to duplicate which makes identifying and fixing it difficult I'll try to do further testing and see if anything sticks.