First question, should it be used?

Second question, how should it be used?

I have a photographer with PR4 who is keen to get up the rankings.

Common keywords:
- 360
- virtual tour
- photography

So i thought, why not use /photography/360degree/virtual_tours/page.html

My concern is that will Google consider that content very deep into the site and not display it,

OR

will Google see the keywords in the URL as a massive bonus and display it further up the rankings?

An issue here is that in order to target one word keywords, you need to be very very relevant, and have good internal linking.
In your case, those keywords are not that easy to attain, so what I would do is to create a content rich landing page for each. And have good external and internal linking with those selected keywords, pointing to those specific landing pages.
Also, one thing to remember. Quantity does not mean quality.
When you target one word keywords, you might get a lot of traffic depending on the keyword, but you see, you also need to worry about how those keywords convert.
You want to get a customer that is ready to purchase, someone that will actually give you $$ for your product.
The disadvantage of targeting one word keywords is that you will get a lot of lookers, but not buyers
From an $$ perspective it is way better to have lets say
a top 10 ranking for "Marlboro Cigarettes" than a top 10 ranking for the keyword "Cigarettes".
The more relevant you are, the better audience you will get.
I have this customer that was also looking for specific one word keywords.
I did get his one word keyword to the top 10, and to tell you the truth, he gets a lot more traffic, but that traffic does not convert at all.
Now he has to worry more about bandwidth :p but me as an SEO I did my job getting him what he wanted.
Talk about that with your client. It really makes sense

mod_rewrite or ISAPI is a great way to clean up dynamic urls. I always recommend it to clients who's system use urls such as ?blah=6t72&blah2=t47there etc.

I haven't seen any major boosts from using it although it definately seems to help indexing especially when multiple variables are passed in the URL.

It can slow your server down if you have a really complex set of rules so use wisely.

I don't think the URL has any bearing on how deep search engines consider the page. I see it more as how far down the page is in the site tree. If it is reachable from the homepage then it doesn't matter if its blah.com/photography/virtual-tours.php or /blah.com/photography/virtual-tours/360degrees/page.php, they are both just 1 click deep.

Hope this helps

SEOMalc.

A MOD REWRITE for a photographer's website is a bit much! Especially if the site is not dynamic with more than 3 parameters in every URL.

The example URL you provided seems to be static and has no parameters.

The URL you gave as an example could be shorter and you want to use hyphens not underscores.

examples:
/photography/360degree/virtual-tour.html

/photography/360degree/virtualtour.html

/photos/360/virtual-tour.html

/photos/360/virtualtour.html

/photo/360/virtualtour.html

By the way, my site ranks pretty high for "portfolio of color photography" as well as a few other terms. Either way, best of luck to you!