My girlfriend and I are both British passport holders and driving a UK registered vehicle on an extended (very) trip around the world. Originally left UK 2004.
After Russia and South Korea we shipped our truck into USA (that was back in NOV 2007.
Our plan was to bounce in and out of USA / Canada / Mexico as and when our 90 days needed renewing.
However, if you exit USA across a land border (ie Mexico or Canada) your 90 day visa does not stop. Bizarre as it also sounds even if you hand it back the authorities do not class this as 'exiting USA' and so they are not obliged to shall we say, 'log you out'.
We found this impossible to believe, but upon checking the US website and then telephoning the consulate in LA it was confirmed, we further enquired at border when we exited and they too agreed it was correct.
So, and this is how the US immigration guy explained it to us; you can enter US, the 90 day clocks starts ticking and you can enter or exit as many times as you wish across either land border but the 90 day clock is not (NOT) affected. Therefore on a return to USA after the original 90 days commenced he suggested that though you be able to enter USA it is in theory possible you could be 'picked up' and classed as 'illegal immigrant'.
Now, for most this is not an issue as 3 months time is more than most can get to explore, for a few of us we have these extended trips and 90 days is nowhere near enough!
Aparently the rule is there to try to curb the bouncing across borders for a day and then back and working illegally in USA, so from US imgration point of view there is a logic. Personaly I feel their logic is flawed and the audacity of one country declaring that leaving it's international boundary is not defined as exiting is for me very odd.
However, that is the situation.
So is there a solution?
Well if you fly out or drive all the way to Guatemala then head back you'll be fine.
& to be fair in reality I doubt a european tourist would have any problems crossing or travelling within USA atall.
What few people know is that you have the option of applying for a tourist visa. Now this little baby is handy. It can have a duration of 10 years (as ours does) and entitles holder to enter USA (as tourist) and stay for up to 180days. Technically you should then leave the country for at least 181days but in our experience this has not been rigorously enforced.
Incidently, this does not get around the issue of land border crossings, but it does give you 180 days to explore and also means your passport has a slightly more validated appearance to any official who feels the need to ponder.
Officially this visa can only be obtained in your home country from the US embassy.
Practically - we got ours in Tijuana, very easy, no problems, couple hoops to jump through, but piece of cake and well worth having.
US is HUGE and has some fantastic scenery to explore, 90 days is nothing !
We are now in Guatemala, planning on few months here exploring central america.
by the way, one further point, by avoiding utilising the visa waiver program it also avoids the registering online malarcky that now surrounds visa waiver.
Which is best option? depends on time you plan to explore North America.
The visa waiver registration online is just another online form filling process (should be free, make sure you are not inadvertently using an agency site who are charging you), shouldn't be an issue and assuming you have no hidden skeletons it will be very easy to get through to US.
For us, without doubt having the 10yr tourist visa is an absolute bonus.