"I SPENT exactly 90 days in the U.S. last summer. I left in accordance with the date stamped in my passport. During that time I worked and had a great time. I am planning on doing the same thing this summer. Will my past stay in the U.S. be held against me? And will this immigration bill that is supposed to be happening be finished in the summer?"
SEEING as you left when you were supposed to - though, of course, the 90-day visa waiver you entered the U.S. on doesn't allow for employment - there shouldn't be any issues with your return this summer.
Bear in mind, however, that when you present yourself for inspection to U.S. Customs and Border Patrol, you will be asked about the nature of your visit, and also possibly asked to provide proof of your ties to home. If you are young and single this is especially true.
Therefore, you should have things such as a letter from an Irish employer, or from a school, stating that you're expected to return to resume your work/studies.
Your question about "the bill" is one that is foremost on many minds now. Will there be a deal in place by summer? Hopefully.
Congress, in conjunction with the White House, is working hard at the present to broker a compromise. Where those negotiations go is anyone's guess at the moment, but it's safe to say that if something doesn't happen soon, the immigration issue will get shunted aside as U.S. presidential politics move even further towards center stage.
Time will tell, as they say.