1. How do you configure your vhosts?
The "Lion way" to do so would be uncommenting the following line in your httpd.conf.
Now you can edit /private/etc/apache2/extra/httpd-vhosts.conf and put your vhosts in there. It's a good idea to start with a default one that will match all unqualified hosts, for example:
Next, you can either add every vhost to the same file, or you can set up a similar system like Debian by including all files in a specific directory next, like so:
Now whether you symlink files here that exist somewhere else (sites-available) or put actual files doesn't really matter. Personally, I think sites-available is overkill for a dev box (and I don't ever really want to "disable" a vhost), so I just create a file for every vhost directly in sites-enabled or equivalent (in fact I named the directory /etc/apache/sites to avoid confusion).
2. Where do you put the code and docroot for your vhosts?
My actual sites I put in /Users/username/Sites. I prefer to put them under my home directory for easier access in Finder etc. That said, it is good to notice that this directory is exposed by default by the userdir module. Since I don't need userdir hosting, and I am going to configure webroots below, I disabled it by commenting the following line:
3. Where do you put the log files?
Log files I keep the same (eg. /var/log/apache/*). Again, for a local development box, I believe individual log files for every vhost are overkill. There's only so much that I can multitask :) If you do want separate log files, you can of course configure it that way inside the VirtualHost directive (for example /var/log/apache/my.project.dev-error.log).
4. Where do you put the local application configuration?
Which applications are you referring to? If web application, I keep those together with all other project files. Depending on your architecture, your config files do not need to be under your webroot if that's an issue, in fact typically my webroot for any given project will be /Users/username/Sites/someproject/web, so config files could be at /Users/username/Sites/someproject/config without exposing them through Apache.
5. How do you resolve the name service?
The most straight-forward would be adding each hostname to /etc/hosts. Unfortunately, this doesn't do wildcards. If you feel comfortable with setting up a DNS server like bind, you could configure one locally or on your network to resolve *.dev to 127.0.0.1, for example. Disadvantage of doing that on your network is of course that it will stop working at a different location. Personally, I use /etc/hosts.