I started feeling the tingling sensation in the first week also...continued throughout. The memory and speech problems came after about 4 months I guess - I started it when it was a new drug and did not realize I was having the speech, spelling and memory problems until friends informed me. It only got worse when I was increased to the optimal dose.
Not to say I did love the drug in that it helped my migraines, but I just couldn't remember anything short term or talk right. Not everyone has the neurological complaints while on the drug and it's very specific (from what I understand) to spelling, short term memory loss and speech problems (meaning you want to say something, but it just can't come out correctly). Mine was by the book and even on optimal dose, never went away.
I was on Topamax for 1.5 years, and it only got worse with each increaseed dose. I work in the medical field so could not ethically continue due to liability issues. I was pretty bummed!
Some people do NOT have side effects, so give it a try - it just may be your miracle drug. With ANY drug there will be side effects most of the time but the migraine narcotics also ruin the lives so it's a catch 22.