i don't know if it makes labour easier but it's one of those thing that they tell you to try if you are over due as they believe some of it's properties can induce labour so they tell you not to drink it until you are VERY close to the end, not 100% but i would talk to midwife?
My midwife told me 36 weeks. It doesn't necessarily bring on labour but more tones the uterus, so you can get stronger Braxtons from taking it. It is also supposed to help the uterus shrink back afterwards reducing bleeding and help your milk come in.
As far as I know raspberry leaf tea tones the uterus as Beccabump says, but lisa85 I think people have been misinforming you - it's not for bringing on labour AFAIK.
I've never taken it, but in general with herbal medicine you are meant to take the 'whole plant' rather than an extract. (This doesn't mean you have to use the flowers and root too, just the leaves if that's the active bit! The point is that when we extract the 'active' ingredient we may well be leaving behind a multitude of other ingredients which are also beneficial to you / complimentary to the 'active' one).
The tea will be much much cheaper, and possibly more effective. You'll need to drink the it several (3-5?) times a day for it to work. As with most herbal remedies, if you really don't like the taste of it, then don't take it - this is your body saying it's not what you need. You can order organic loose leaf tea from Baldwins & Co who are the quality supplier. It's £1.49 for 25g.
Capsules are more convenient of course, but may not be as effective IMO. Baldwins do capsules too but these are £7.95 for 60.