This might be of interest:

UK residents buying goods on the internet from the US won't have to pay duty on purchases worth less than £105, under new rules from HM Revenues and Customs. Until now, duty had to be paid on goods bought from non-EU countries that were worth £18 or more. That limit is being extended to £105 from 1 December. However, VAT will still be charged on goods worth £18 or more.
PC Pro: News: Duty limit raised on net shopping

The official page hasn't been updated yet though.