This is a follow-up to my previous post on JBOWS. It seems some others are touting the role of the ESB as well. Learning from SOA Mistakes and Avoid SOA Pitfalls both go into some detail about the role of the ESB. The main point both make is it helps you avoid JBOWS and the same old brittle architecture of the past.
The bottom line is this, implementing a bunch of Web Services without something in the middle is going to leave you with a standards oriented mess. Let's call that SOM. Pronounce it like some, as in that is SOM fine architecture you can up with.