I just felt obligated to share my experience because it was so positive: i have been on 600-750mg since 2005. I suffer no side effects (i cannot even tell if i have taken it) and my incidence of illness fell by 90% for the last 8 years (i asked GSK if they had ever heard of this but they declined to comment). I did forget my meds on a trip out of the country once- i had no withdrawal but after 24 hours i felt sluggish and had trouble getting things done plus my old sugar craving returned. Once i was back on it - everything was normal.
One comment on the dose (which is higher than you typically see): the doctor who prescribed it told me that the original clinical trials were at 900mg (that was what GSK found to be the effective dose) but since 5% of patients had seizures at 900 they dumbed it down to a max of 450 where the seizure percentage dropped to 0.1 (1 in 1000) so it would be more marketable (hard to sell a drug that caused 1 on 20 to have a seizure).