Of first-to-file, one notes that such a system favors those with more resources (e.g., large companies) over those with fewer resources (e.g., independent inventors). While this may fit the culture of Europe or Japan, it's not clear that it's such a good idea for the small inventors of the U.S. Although it has been pointed out that "small inventors" lose more frequently than win in the current patent interference system, this argument does not negate the idea that small inventors may be even worse off in a first to file system. That is, saying that small inventors don't do well in "first to invent" is not a comment on how small inventors will do in "first to file" and the absence of comment does suggest that it is understood that small inventors won't do well in first to file.
Of oppositions, a number of attorneys, including Joseph Hosteny and Cecil Quillen, are against the the postgrant opposition system. As noted on IPBiz on July 6, there is literature showing that oppositions may not be the way to go in the United States:
Dale L. Carlson and Robert A. Migliorini presented PAST AS PROLOGUE FOR PATENT REFORM: EXPERIENCE IN JAPAN WITH OPPOSITIONS SUGGESTS AN ALTERNATIVE APPROACH FOR THE U.S. [88 JPTOS 101 (Feb. 06)] and Patent Reform at the Crossroads: Experience in the Far East with Oppositions Suggests an Alternative Approach for the United States [7 N.C. J.L. & Tech. 261] but few people in patent reform are getting the message.
It's not clear that the Hatch/Leahy bill has factored in the identified problems with first-to-file and the postgrant opposition process.
On a separate note, I have submitted a law review article showing that the methodology of Quillen and Webster - III (Fed Cir B J 2006) on patent grant rate is flawed, and that the elevated numbers asserted for patent grant rate for the USPTO are not correct.