There's a lot of ambiguity there, actually. Many people argue that the DMCA, as written, forbids any circumvention of DRM, even for personal use. In any case, while individual consumers are unlikely to have any problems, even if it is illegal, the people who make the tools to do it have often been attacked -- look at DVD Shrink. They had a ton of problems offering their DVD ripping software.
I think the issue here is: it's only a problem if you circumvent DRM and someone finds out about it... in other words, if you bypass DRM in order to transfer a file from one ereader to another you are unlikely to come under the eye of anyone looking for rights violations. However, if you upload the file to a torrent site, then chances are you will be caught.
It's like some elements of kinky sex can be prosecuted as GBH but they only get prosecuted if one of the participants presses charges or you do it in a place where the police have no choice but to 'see it' and take action. The acts are illegal but you won't get charged if the police never see you do it...
So it is not so much illegal to mess with DRM but some things you might do afterwards are illegal and breaking DRM might be construed as 'suspicious' if anyone finds out about it.
Oh, and referring to an earlier point, £5.99 is about $12 - £14, depending on what the current exchange rate is. The usual conversion is to roughly halve dollars to get pounds. Though there are also issues of relative economies to take into account here - some things here have been expensive for a long time that may well be a lot cheaper in the US (I think books are one of them)
And yes, I do beleive we have an issue of undervaluing ebooks...
