The Boston Public Garden is still a major landmark and tourist attraction! But also the book mentions a lot of specific streets, so you can find everything on the map -- the Church of the Advent, where I was a bellringer when I lived in Boston, is in that neighborhood, so I know it pretty well.

It's a historic neighborhood, so the buildings haven't changed much, though the specific businesses have (the Ritz-Carlton has been through multiple name/ownership changes), probably the main change is that (like many parts of the Boston area) it's gotten substantially safer to be out at night. I also don't think of the Public Garden as being populated by bag ladies, but I'm not sure I'd know a "bag lady" if I saw one (most of the visibly homeless people I remember from the Boston area were male panhandlers).

(This is in striking contrast to the visit to the North End in Anastasia, At Your Service, which between the Big Dig and gentrification has been completely transformed, even if many of the buildings are still there.)