Well, I just love to tip on Reddit and I also use my personal Url -->
http://Kprawn.tip.me in other forums, where it's not incorporated within their software yet.
I think the best thing to do, would be to make sure, you tip enough to make sure, they can buy something usefull with it. After you tipped someone, also include the following :
* You can spend money I just send you here :
www.overstock.com /
www.Dell.com etc.. etc.. {Include the link to a cool site, where she/he can spend the coins}
For people to accept a new currency or technology, is a big thing already.... make it easy for them and suggest some merchants accepting Bitcoin. The worst thing will be, when people accept the currency and they want to spend it, and the place where they want to spend it, does not accept BTC.
So make it FUN and easy for them .... ;-> Tipping someone 0.20 cents will not encourage them to use it.... Rather tip them $1 to $5 and more if you know them on their Birthday and make it worth it.
Remember, if they did not accept the tip, within a few days, it will be cancelled, and it will go back to your Changetip account. {So you have nothing to loose}