I know what you mean if isn't acknowledged within the hour I start going nervous

They could give you some crap if you do that. They could count that as a special rule, which is not allowed unless you're doing a private giveaway.
They are even people who refuse to befriend the gifter and insist that that counts as a "special rule" and the gift/key should be sent only through their e-mail.

You should do this and maybe it will save you some headache and you can also give the gift/key via steam chat, if the winner didn't connect in 48h, then you'll still have the key and can ask for a reroll.

just goes to prove there are some sad fuckers in the world - me giving is supposed to make me happy !

As far as I know you may set specific requirements for group giveaways as well. Public giveaways, well, under such circumstances they own you big time.

My favorite thread about people giving crap to someone who offers them a game for free:
http://www.steamgifts.com/forum/oq0FY/is-this-legit-when-someone-says

BlackDawn is probably right, though.

I can confirm that you can set rules for group and private giveaway.

ok peeps, i dont want to set any rules on my giveaways, but when u spent £30 to give away a game that is a key, and I have not heard back after 5 days, and i cannot check to see if the game has been redeemed, i hope u can understand my concern ?

I would be to but I guess the most you can do is reroll for another winner and just tell the new winner that it might not work and I am sure we would all understand if it didn't

Ouch. Ian. I feel for you. :( That is not a good situation to have.

I think a solution down the road is to receive your Steam gift and add it in your inventory. So you can still verify if the gift in your inventory is taken or not when you send it over.

I say we all add the user and spam! Heheh!
*JOKING!

Here's what I've started to do for my giveaways on SG, Ian, after running into the same kinds of issues you are experiencing.

Before the giveaway closes, I look at the library for people who enter to make sure they don't already have the game. If they do, I would send a message to SG support (this has not happened to me yet but I've heard of it happening). People should know what they have in their collection and not be entering for games they already have.
I know that can be a chore for you since your giveaways are always very popular with over 100 entrants at times. Mine don't get nearly the same amount as yours so its more manageable unless its a public GA.

After it closes, I doublecheck the winners library again to make sure they don't have it.
I send them a friend request.
If they are online, I contact them and give them the key and remind them to mark it as received.
If they are offline, I send them an offline message to contact me when they come online so I can get them the key in live chat. I screenshot this in case I need to send this to SG to let them know I've done my part to try to contact the winner.
I do the same the next day and the next and so on. If it gets to be 5 or more days, which it has, I start telling them the GA will be rerolled per SG rules if they don't do their part to contact me. Only once has someone waited till the very last day.

After the 7 days, I check their inventory again, to make sure they've entered the key and the game is in their inventory. If it is not, like what happened with my last 2 giveaways, I again send them a message to use the key. Again, in my last 2 giveaways, one guy finally did on the 14th and last day I was giving him before notifying SG support. The other winner never downloaded his game and he has since been suspended by SG for multiple violations.
Next time, I'm not even gonna give them 14 days. Its 7 days per the rules.

See, these are the kinds of things you expect to deal with in a public free-for-all giveaway. Not a group/community giveaway. Its almost not worth the hassle lately for myself or with the things I read on this thread. Our giftclub is rather impersonal anyways, much more than the GOG forums if you think about it. For the giveaways I've made or the ones I enter, I don't even know 75% or more of the names in there. Not to stir anything up but I'd rather my gifts go to people contributing to this community and not those who get up to 40 rep, join and then we never hear from them again. We can't even find them on GOG to gift the game to as an alternate option to email or Steam chat.

As for 48 hours, not sure if you can enforce that since SG themselves say 7 days and not any lower. I think the kind of rules you can set are if the gift is a bundle, the winner or entrants can't have a certain amount of the games already and you would rather the winner have none or a limited number from the bundle. You can set contrib value. You can ask them to make their profile public. And some other things. But I'm pretty sure the 7 days is a rule for everybody, private or public.

I'm sorry for you, Ian, that you have to be all troubled and concern about this. But you sent the gift to the winner, meaning that you can see who won. If you click on his/her name, you can see his/her profile, and from there you can see if he/she was online since you sent the gift. If he/she was online more than 5 days ago then maybe something happened to him/her. But if it less, then he/she clearly saw that he/she won on SteamGifts. From his/her profile you can access his/her Steam profile page, and if it is public, you can see if the game was redeemed while looking at his/her games. If that's the case, I would contact the SteamGifts Support ASAP for assistance for this problem.

You have to contact SG support to get permission to do a reroll. And if you've already supplied the key in email or any other form, they will not allow the reroll. They only allow it for a variety of reasons as long as the key has not been given out.
So at that point, your best bet is to have SG admins mark your gift as received and once that is done, maybe drop the key in the ninja or other thread and tell the people it may not work.
But again, this all can only be done once the 7 days have passed.