Some early thoughts on selling ebooks:
1: it's an impulse-driven market, particularly in the UK
2: price is paramount (see above: $2.99 works in the US but not in the UK)
3: readers don't care one iota about an author's sales track
4: Amazon doesn't care one iota about an author's sales track
5: to sell ebooks, it helps to go where readers of ebooks hang out
6: an Amazon customer review is priceless
7: Amazon know how to sell books
8: the more you sell, the more you sell
9: promotion is much more efficient and enjoyable when you have access to your sales figures
10: the US and the UK are completely different markets and it's extremely rare to do well in both
Feel free to add your own thoughts in the comments.