Thanks for the solid feedback so far - agree with lots of what's been said. I would clearly be thrilled to match at any of them (and many others, these were just similar ones that came up for me and other people i talked to). My two cents:
BIDMC -
Pos Thoughtfully designed residency by Rosen and Wolfe aiming for high yield training without the crap, really think the 3+1 is a fantastic concept (and truly a 3+1 where 4th year serve 1/2 time jr attending with equivalent salary plus 1/2 time academic pursuit including MPH/MPP/etc for the +1 vs other places who market a 3+1 which is really a 4), strong independence managing dept in 3rd year, best IT/workflow anywhere, powerful academic setting BI with high acuity/sick older medical population with decent amoutn of time at several community sites that fill in the experiences, links to Harvard resources, lots of opportunities for research and other projects but didn't seem too heavy handed, awesome group of residents who are interested, interesting, and balanced, and supported incredibly well financially and emotionally by program, growing opps for int'l; relatively young program but strong reputation already
Neg Boston weather, considerably older population at BI (although this could be + or -), didn't seem as US heavy as other places, less int'l/global involvement (but growing, sweet!)
Harbor
Pos Incredible clinical training/setting/population, really high volume, super high acuity, intense ER training with early development of independence but with really involved and dedicated attending support, serving lower income/underserved Hispanic/AA communities, solild exposure to trauma, amazing residents again as BI and Stanford, brilliant, passionate, but also just damn cool people who know how to have a good time and support each other, close to beach communities, long history of success with great alum base
Neg LA traffic, lots of off service 1st year including ward time, hectic/cramped/perhaps insane ED (although getting new ED summer '12 I believe), somewhat more traditional didactices although changing, and the move to a 4 year program which has been nicely discussed (appreciated the PD's honesty about needing a 4 year for staffing the new ED volume, but underscores the volume and flow problems in the current setup)
Stanford
Pos Great mix of clinical sites really unique in residencies (their county has really surprising high volume, high acuity, lots of trauma, underserved Hispanic/Asian community; Kaiser provides more community model with interesting integration and efficiency of Kaiser system in beautiful new hospital; Stanford has very academic/tertiary setting with wonderful opps to learn from consultants, etc), fantastic int'l opps, great wilderness leadership, good US division, good sim/education division, significant amount of elective and research time for 3 year program, also amazing residents like other 2 - smart, passionate, but friendly, collegial; program really takes care of residents probably #1 of any place I've seen from $ and benefits to faculty support, would kill to move to the Bay Area
Neg Most time is at Stanford which has it's +/- - more involvement of consultants, more tertiary style of practice, less efficient, lower acuity of patients, frustrating design of ED I think from what I saw (although again balanced with other sites well); academic culture (can be +/-), good but not great reputation across country? A 3 hour tour 2nd only to Gilligan's island (not that interview day tours matter)