I would encourage you to look at the Cliff Site in late December of go by their booth at the expo. Each group leader has a style they run. It may be straight through, walk at the mile point, walk at aid stations, or walk at discrete time intervals. You can usually work around their styles if different that what you trained for with a little thought (ie if you run a mile walk a minute and your group is running straight through, you know you will need to either work ahead of the group while you are running then restart once caught. Ot run at the tail of the group and allow the froup to pull away during your walk, catching the group as you come back on run.
Cliff and most other pace groups will ask folks entering their gorup to wear a pace time bib on the back of their jersey. Its an easy way to identify the group. Not all in the group will have the time bibs. Personally, if you are looking for a stretch time with a group do not put the time bib on. Its a sad site to pass a 3:45 bib as you click by on a 4:15 pace.
My final word of advice about pace groups is to remember that you are in charge of your race. Many folks will over estimate the challenges of their first attempt at a marathon and keep up with a group that is faster than their capabilities for 10-12 miles; only to have the wheels fall off and enter death march mode early. It is not a fun marathon at that point.
