Here is one trick to greatly speedup asp.net compiler. First of all, assume you have enough RAM to give about 512Mb for this. RAM is cheap, so you always can visit store and buy it. And your time is priceless. 

Idea is in creating RAM drive and pointing asp.net compiler temp there. To create RAM drive you need to download following free software

http://www.ltr-data.se/opencode.html#ImDisk

IMDisk - awesome thing. Install it.

Now create ramdrive.cmd somewhere ( for example c:\ramdrive.cmd ) with following content

imdisk -a -s 512Mb -m R: -p "/fs:ntfs /q /y"  

create a shortcut and add it to Startup

Now everytime you start PC you'll see quick console window and you'll got a new drive "R"

Ok. Now you need to change your temp settings

Edit this file: C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\CONFIG\web.config  

( I assume that you've Windows installed in C:\Windows . Change path if it's different )

 In this file you need to add attribute to <compilation> tag

After change it should look like this: 

        <compilation tempDirectory="r:/asp.net_temp" > 

That's all. Now you can build your asp.net projects much faster. You can try to point all windows Temp on that RAM drive, but I haven't gone this far yet.