Cleanly scaling up blueprints/etc.
I saw that someone was tracing low-res blueprints in AutoCAD, and I felt his pain, as I've had to deal with that a number of times in the past. Fortunately, there are some new software tools available to help with that.
A long while ago, I evaluated some software for a client to resize pics without losing detail, and find that Genuine Fractals 6.0 ($160), PhotoZoom Pro 2 ($240), and Image Enlarger 0.8 ($0) do an amazing job of producing sharp, clear enlargements, as can be seen in this comparison of a 64×64 sample enlarged to 256×256 (4x):
For rescaling high-contrast/non anti-aliased images by 2, 3, & 4 times, however, there is simply no better algorithm than HQx (Code page)
Which one will work best for your project will depend on what kind of source you have, but I've found both the SmillaEnlarger and HQx to work wonders when the artwork I have to trace is just too small on its own.
Hope this helps!