One foot - good luck for tomorrow. How many weeks will you be.
Amy - glad to hear you are feeling better, hopefully this is the turning point 
West - how are you feeling this morning?
Sasha - 6 weeks is entirely possible for me, so I guess I'm clinging on to that. Although no fetal pole is an ominous sign and We are still expecting bad news. Below are the links I have been looking at just in case you haven't see them yet.
www.brooksidepress.org/Products/Military_OBGYN/Ultrasound/1st_trimester_ultrasound_scannin.htm
radiopaedia.org/articles/failed-early-pregnancy
www.ultrasoundpaedia.com/normal-1sttrimester/
americanpregnancy.org/pregnancy-complications/early-fetal-development/
www.nhs.uk/news/2011/10october/pages/ultrasound-scan-miscarriage-early-pregnancy.aspxk
www.nice.org.uk/guidance/cg154/chapter/1-recommendations
Basically all the research I have done indicated that these tests seem to have a variable margin of tolerance/error dependent upon the study, particularly when scanning before 8/9 weeks. Interestingly NICE are currently reviewing its clinical protocols for early pregnancy tolerance parameters following a study into potential misdiagnosis of miscarriage of a very, very small percentage of cases. All this says to me at such an early stage you need to be absolutely certain before you make any decisions for medical management if you think the dates may be possible. In my last miscarriage I knew that wasn't the case as I would have had a positive pregnancy test before I conceived.