I used to have...I think 12 vials drawn a few years ago, every three months. After getting out of that mess, I only get blood drawn once a year, a couple vials or so now.
Or of the nurse being unable to find a vein and having to try again and again and again and again.
Also, the nice bruise you can sometimes get afterwards.
^Happened to me
On my right arm, the bruise(both of which I've had for years now) is from my joint to about 1/3rd up my arm, on my left, it's the size of two fingers. Hurt quite a bit, but I didn't have anything afterwards except pain and being a bit dizzy.
Anyways, good luck, shouldn't be terrible but it depends who you get. Some do it quickly, don't bruise at all with no pain, others take five plus minutes to even find a vein, then constant poking.