I'm very impressed by these Anker batteries, well made, run as cool or cooler than the standard battery, and even after just 3 charges i'm noticing they last a bit longer each time. My Galaxy S2 is down to 20% (its nearly 8pm now, took off charge at 6am this morning) but ive used it alot today, 3hrs music, emails, text, twitter, surfing net, downloading tunes for 1hr over wifi and alot of playing around so the display is lit up.
I bought these with some doubt as to whether its worth having, but now i'm very glad i did, having a full battery ready to pop into the phone is great!
Postage even though it wasn't displaying until checkout was £2.75 but i signed up to the trial for 'Amazon prime' so it was free one day delivery!
Overall a good purchase, good quality batteries and good charger. Recommended!
*EDIT/UPDATE
I've used these for a while now and can still recommend them. Few things i have noticed. They take around 6hrs to fully charge from around 5%, but so does the standard battery(thereabouts) so probably more to do with the charger(i dont charge up using the original charger, prefere to swap batteries and then charge the flat one using this charger) they do indeed last noticeably longer than a standard genuine battery, but tend to drop their charge if not used, roughly 1-2% a day, so it'll be only 94% if you dont use it for 3 days or so since fully charging. Most life ive got so far is 42hrs with the phone always on and normal usage, compared to 38hrs with the original samsung battery, i always favour using these instead of the original one now.
Use the 'Powermax' app from android market to seriously extend battery life