There's been some interesting discussion recently about the merits (or not !) of analogue summing - for example over at the Recording Revolution site. Make sure you read all the comments !
For once I'm not going to tell you what my own opinion is, though - just make some observations from where I sit.

First, some facts:

• I've mastered thousands of albums, over the years, and I've talked to hundreds of engineers - maybe tens of hundreds
• A few times a year, I work on great mixes. Often I work on very good mixes. Most often though, I work on mixes that are OK, but have some room for improvement
• A lot of stuff these days is mixed "in the box", a few use analogue consoles, and some use analogue summing

Now, a few observations:

• Those different standards of mix - great, good and OK - are equally spread across analogue and digital summing setups, as far as I can tell
• None of the people who use analogue ever ask me "do you think I should go digital ?" (*)
• Whereas people who work in the box sometimes ask me about analogue summing

(*) Although many of them say "I can work in the box if necessary, I just prefer not to"

BUT

I've never had someone ask "should I try analogue summing ?" and thought to myself that changing to analogue summing was the most important thing they could do to improve their sound. Not even close.

People who ask that question would always get more benefit from better players, better instruments, better arrangements, better mics, a better room or better monitoring - in my opinion.

The people making great mixes never even ask this question - whether they sum in analogue or digital.

Feel free to draw your own conclusions : )