For architectural shots you will want the relationship between the tilt and shift movement moved 90° from the factory standard configuration.

As an architectural photographer I can assure you that isn't necessary at all. The 24mm PC-E is a great lens and I find out of all the movements I use rise the most. Having used it on cropped frame DSLRs it is severely limited for architectural photography with this setup, not only because of the limitations for rise but also because it isn't wide enough on these cameras. On my D700 it is amazing though. I have been published in many magazines and calendars with shots taken on this lens, it's one of my favourites! Definitely pair it with the right camera though.

The need for both tilt and shift for architectural work is dependent on the camera position relative to the subject. The best results for the classic example of the tall building shot from street level are obtained by combining shift to straighten the lines of the structure with tilt in the same direction to align the plane of focus with the face of the building. The writings of the world's most well known architectural photographers almost universally agree on this point. While tilt may not be necessary in every architectural photo you might want to take, it will be beneficial for many.

True and on a 5x4 view camera or larger this is especailly important but personally I've found the difference in depth of field if already using a small aperture on a DSLR (especially if cropped sensor format) is unnoticeable even at actual pixels. For me it definitely doesn't warrant the extra cost of having the lens converted.

There are a lot of purists in this field and there are many who probably think my logic is strange here but it's all relative to the medium you're working with. I work at f11 - f16 most of the time for example because I've found that this particular lens is much sharper at these apertures than when stopped down to f32 for instance. Photographs are about perception and I find sometimes a sharper image gives the illusion of even more depth of field than a less defined image taken with the smallest aperture. Photography is also about personal preference. Using my DSLR I find that rise is mostly all I need for architecture. You can after all use focus stacking in post processing if you really need to obtain extensive DOF.

If focus and quality is really that critical to you and you want to employ the full techniques of the Scheimpflug principle in your everyday work then surely you'd be working with a digital large format of some sort not an SLR anyway.