For new grads/residents...
The "buy-in" is usually deducted from your salary. So, essentially you pay as you go and you never really miss the money. Usually once you are a partner you share the subsequent new hires buy-in money so you eventually get it back anyway. When I was looking at jobs as a new grad I had no problems with a buy-in. Remember the people who are partners have built this business from the ground up. I think it's unreasonable to expect to come out of residency and walk into a job with total financial and voting equality with members who may have been there 20+ years. That being said, do your homework regarding partnership availability, financial disclosure, who gets what monies, etc. No scrupulous group would (or should) withold partnership from a competent, hard working new hire. Before you sign get clear info on how partnerships are granted, voted on, merited, witheld, etc. Any group that invests 1-2 years in you is going to want to keep you on as a partner. If there are problems (i.e. professionalism, practice patterns, personality conflicts) they should be made clear to the candidate LONG before the partnership question is even raised.
For those considering groups with no buy-in...great but consider this - if you aren't buying in to a group be mindful of where the money is going, someone is probably making bank of of your hard work. Also, if there is no buy-in, what value does the group hold? Which can raise qustions about the groups long term viability/stability.
Not saying to ignore these groups, often they have great deals but just beware and ask, ask, ask before you sign.
Good luck!