Re: To block or not to block
'Blocking' someone with any idea about martial arts is pretty stupid. The hand can direct, guide or contact the incoming arm, but a forceful block is just asking for a follow through with the elbow or shoulder or a counter technique.
Generally you move in vigorously with a feeling of over-coming the uke and making contact as soon as possible (preferably before the down swing). If uke is intimidated by this you can follow his retreating movement and do something like irimi ikkyo. However often the strike is too fast or strong so you open the gap as they strike down. They should feel like they are going to hit you and make contact with a big block, but the block isn't there; as they cut down you allow them to, whilst moving to the side. Aikido is blending! It's all about getting that connection with uke, allowing uke to do what he wants, but keeping you posture correct and protecting yourself.
Cutting down hard may be unbalancing for you because really it should just tip uke (and you shoudl remain straight). Don't substitute force for timing!