This is how I see these PCs:
BRAND-IN-A-BOX: Good for cheap, but not cheap for good.
ALL-IN-ONE: Combines the weaknesses of desktops (lack of mobility) with the weaknesses of craptops (expensive and weak with limited cooling and no upgrade path).
They're ok for use in businesses because office apps aren't exactly what I would call "hardware-intensive" and they're ok for the home-uses of the non-tech-savvy but that's about it.
They also tend to be loaded with bloatware and use the incomplete "Home" versions of Windows that I often think were made with Baby-Boomers in mind. I remember one of my earliest craptops had an OS on it called "Windows Vista Home Basic". It was so bad that I had to scrounge to find XP drivers for it. Fortunately, because it was an eMachines, there was an Acer Aspire model that was literally identical and I was able to find XP drivers for it. Its performance with XP Pro was like night and day compared to Vista Home Basic which had rendered it borderline unusable.
I wanted the craptop primarily for OpenOffice and Firefox but even those programs were laggy with Vista Home Basic. If I weren't a PC expert, I would've been royally screwed and would've had to just deal with the crap that they gave me.
The only brand-name desktop PC that I've ever owned... Well, that's not the right way to say it because I've never personally owned a brand-name desktop but my family had an IBM PC model 5150 and my mother had some eMachines thing back in 2000. Those are the only two brand-name desktop PCs that have ever existed in my family (if you don't count the two TRS-80 Color Computers that we had before the IBM PC).