There are a few good looking channels surfacing now, with cDiscount and Allegro being pulled to the forefront from my own point of view as our software provider will soon be offering these as integrated channels.
To be fair, you can't really beat having your eBay listings shown internationally and opening up the Unified potential through your Amazon. But as Page correctly said above;
different countries have different prefered channels
cDiscount isn't just a French marketplace, they also operate in a number of countries including Brazil, Thailand and Columbia. Ordinarily I would have looked at those locations in the world and dismissed them because my organisation never really has orders from those parts of the world. And yet cDiscount operates a channel for those territories which would suggest that in some way there is a demand for online services. And the fact that we never get orders from those parts of the world would suggest that either we don't offer what they want or that they do not use eBay and Amazon.
I have posted a fairly extensive (aka long

) post on cDiscount which I'm not allowed to link to because of the link/post count limitation of the forum, but I have had all in all a fairly decent experience with cDiscount.
I would say that expansion into Europe could start to be the future for a lot of UK based ecommerce companies. But I might go so far as to say that maybe even limiting to Europe might still be too small. Within Urban Trading, we have links to America, Canada and shortly Mexico through our single Amazon.com seller account. Three channels which cover a fairly large area of the planet and in my opinion hold huge potential. We are currently also looking into Amazon India which is another economy which is growing in leaps and bounds in terms of online sales.
As always there are no easy answers. Only you know your circumstances and only you will know after you've done research whether a channel is viable for you. But expansion is rarely ever a bad thing if it's researched and done properly. For UK only Amazon sellers I would recommend opening up to Europe through the Unified Amazon accounts. These extra channels under the umbrella of the UK account don't, as far as I am aware, cost you anything more apart from the normal selling fees that Amazon have for UK. For UK only eBay sellers, start opening up some of your listings to Europe to gauge the market. This may include extra fees that your pricing may need to accommodate, but should be easily worked around. For anyone already in Europe with either eBay or Amazon, looking at channels external to Amazon and eBay is a definite option. As is expanding globally rather than staying in the confines of Europe. It all depends on your outlook; nothing ventured nothing gained? Or better safe than sorry? So far, for Urban Trading the risk has been rewarded and we are doing consistently ok. We could always hope for more, but it could most certainly be a lot, lot less.