Yes, I've seen a lot of conflicting advice too.....I think the old adage 'everything in moderation' applies here.

Care should be taken not to add to much directly to the soil as it can make the conditions too alkaline and avoid ash from treated or painted wood which may contain toxic trace elements.
Other than that, I regularly add wood ash to my soil in small amounts and the plants seem to thrive. I also add it to my compost when I did it out from a "cooked" heap rather than adding a bin full on top of the plant material. If the layer added is too think it does just sit there unless you can turn the heap well.
See http:www.gardeningforeveryman.com/gardencompost.php for more information on composting.

I agree with gardenmad1. If the wood is treatment free (unpainted etc.) and you can mix it well with your other compost it will do it a lot of good.
It is also good for helping to break up clay soils but as above it can make your soil to alkaline.

Aaah thank you GardenMad and Ian. No treated wood - just tree cuttings, so I'm safe! That's really useful to know - I'll stick some over in the clay-y part of the garden :)

Thanks!