how regional results differ from google.com

[fizzycherry]

i have tried reading the faq and searching the site for the answer to my question but had no luck. it seems pretty standard to me though so apologies if this has been dealt with often!

basically, i am considering 3 types of searches:
1. search at google.com
2. search at a regional google e.g. google.ie within that country
3. search at regional google with the "search pages from ireland" etc option selected within that country
4. searching at regional google from outside that region

from doing a couple of test searches, it seems the results from conducting the first 2 types of searches are the same? will i only see different results at a regional google if i limit results to be from that region?
as regards type 4, will someone who say searches google.ie from america see different results to the ones i see sitting in ireland?

thanks in advance!