After searching in vain for this information, I have set about to identify, by size and estimated length, the vacuum hose necessary to replace everything under the hood on my 2001 S60 2.4T. What follows is what I came up with, and how I got there. The lengths are estimates, as I did not pull the hoses off to measure, but used a tape measure from the top of the engine, and erred on the side of more, not less. I have not yet crawled around to find where all the hoses end up, so input where you know something looks wrong will be greatly appreciated. Also, I'm in California, so when I say driver's side its left side drive car.

The Totals:

5mm - 3 feet plus 2 clamps
6mm - 7 feet (per IPD) plus 5 or 6 clamps
8mm - 3 feet (plus 6 feet and maybe 2 clamps if you replace a plastic hose described below)
10mm - 3 feet plus 6 clamps

Here is how I got there.

First, and simplest, are the 3 hoses to the Turbo Control Valve. IPD, who has no doubt worked on a few more Volvos than me (one total) says you need 7 feet for this. I believe them. The fittings on the TCV measure 6mm. Only two of the three hoses were clamped at my TCV, and I assume that all 3 are clamped on the turbo, hence 5 or 6 clamps.

There are three hoses connecting to the intake manifold. The first is a small hose at the driver-side end of the manifold. The fitting faces the firewall and measures 5mm. The hose runs to somewhere back near the Turbo, and is clamped. The length of this hose is approximately 3 feet.

The second hose off the intake manifold comes out of the midddle of the manifold next to the fuel line and runs to a T connection to the driver's side of the engine. The fitting measures 8mm, and the total length of this section is approximately 1 foot.

The third hose off the intake manifold is also off the driver's side end, and is significantly larger. The fitting measures 10mm. It runs about 3 inches into a Y valve, and from there branches (a) down to the pipe running to the throttle body and (b) to the brake booster. Total length is about 3 feet for the three sections, and each is clamped at both ends (6 clamps).

Finally, there is what I think is the boost pressure sensor that is clipped near the top of the driver's side of the radiator fan. It has 2 hoses connected to it (and an electrical connector). The fitting is 8mm, and the short hose runs to the same T connection as the second hose off the intake manifold. From there, it runs back to the air pipe that runs out of the air-filter box. Total length of the two portions is approximately 2 feet, and I found no clamps at all.

The second hose connecting to this sensor has a short section which then connects to a plastic pipe. The plastic runs near the radiator fan to the bottom of the engine, heads to the passenger side, then to the back of the engine, and appears to head to the vicinity of the turbo. I estimated this plastic piping to be about 6 feet total, though I do not know if it can be replaced with vacuum hose. If it is anything like all the other plastic pieces I have found under the hood, which are all baked brittle, I hope it can be replaced with a hose.

So what have I missed (before I go out and order $100 worth of hoses and clamps)?