Well, I'm not saying that there aren't better tools, but I didn't find SpeedDisk that bad - it did what I wanted (important note: on Win98). I also use CleanSweep for a long time and never had any stability problems with it; I admit that you should be careful when uninstallaing something (sometimes, it wants to delete things that should be kept, so you'd better know what you're doing) - but it never crashed for me. Sometimes, it doesn't detect all the changes done to registry, but I'm not sure if it's not rather a Windows problem.
I find NDD perfectly OK for routine checks, cleaning of lost clusters, long filenames, etc. (FAT). Of course, I would never let it repair a seriously damaged partition (that's where DiskEdit comes
)
Registry Optimization wizard is handy sometimes as well... WipeInfo maybe, if you know what you're doing.
On the other hand, I never felt like I'd need Ghost for anything
So, I find NU a collection of simple tools. Sure, there are better ones - but usually not in a package (i.e. searching for and installing many tools would be needed). Just my personal opinion, of course.