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What Iserth and Centauri said. 

Why do you want to use one of the effects, what is your goal with this effect? Is there something specific you want to accomplish.

If you must railroad your players another "in the rules" option would be to use the character motivations optional rules from DMG2 with the character's normal motivations over ridden by the geas effect.

The way I see that it could be used with out upsetting some players is if it's like the labours of Herakleas and the geas that appeare in Irish tradition. Less a curse thrown by someone else but a willingly accepted punishment to keep yourself honest. 

Gonna have to agree with LunarSavage though I'll be a little more...restrained in my condemnation

First to answer a question of "WTF is this supposed to emulate?!"...well, Hercules and his labors is a great example.

Second this all depends on how things are done. If the situation arises where a player fails a save and gets hit with a Geas or whathaveyou that is a case of "crud happens". My players would take it as an opportunity (like they treat everything) to see where it goes. After all, it's almost certainly going to be something dangerous...and dangerous things are rewarded by the mechanics of the game itself. They will get loots & XPs. Hooray! It also gives them plenty of potential drama and that makes for interesting times.

The problem arises when tables blur the line into a "narrative" model where there is a story to derail or to force...so a Geas either derails an existing story narrative by taking it in a sudden different direction or it forces a story narrative onto the players by giving them an in-game force compelling them. This, of course, is all caused by the existence of a pre-conceived story...and there-in lies the actual problem. If there IS NO STORY then there is nothing to derail or to force. Instead, a geas or quest simply becomes a new event/situation for the PCs to deal with in whatever way they so choose. It is not the DM giggling as he enacts part of his master plan, it is simply an NPC taking an action that would make sense for the NPC to do.

And fair is fair...I've also had players use geas/quest to great effect.

Curses are similar to this. In fact, one of my players started my current game with a powerful curse on him involving a weighted stone around his neck. And he did so at his own request because he had a cool idea. Interestingly enough, he fully expected this curse to last a while since Remove Curse requires at least a 5th level cleric and those aren't super common AND most won't just cast such a powerful miracle for free. Well, they happened to randomly stumble upon a group of friendly hobgoblins who randomly had a 5th level cleric of the hobgoblin god-king in their company. After they fought alongside each other, the hob cleric took a whack at removing the curse stating that his was the most powerful god...I rolled...Nat-20...the stone dropped off. This happened in like the 8th or 9th session. Everyone was flabberghasted...heck I was shocked! It was awesome!

That lead to the hobgoblin telling the PC that he must travel to the hobgoblin capital within 1 year and offer up his service to the god-king to fulfill one task. Now, no geas or quest was involved in this...it was just something the hobgoblin stated as compensation...and the player embraced it whole-heartedly. It's becoming one of his most repeated talking points both in and out of character and something he references constantly some-20 or so sessions later.

They then turned the tables on Curses by using one to weaken a dwarf assassin released into their custody to help them find someone else. What was good for the goose became good for the gander. And that was cool too!

So, like so much, I will say ithat Geas/Quests can become a major issue when a story is presumed (or being preciously crafted by a wannabenovelist...uh I mean Dungeon Master)...they can also become an issue when players take game-events personally instead of accepting the game as a game and using the events of the game to craft interesting situations for themselves. After all, there's a big difference between exclaiming "That sucks!" and claiming "That isn't fair!"...the first can be legitimate but doesn't mean it has to be negative...the latter is usually someone acting out because something in a GAME hasn't gone their way...which is a sign of immaturity.