So say I had a Q6600 C2 Quad with a 4870 and I wanted to upgrade..I go buy a nice Gigabyte Z77-D3H ($125), and and i5 3750k ($250) for $375 I have a new overclockable computer w/USB 3/SATA 3. No need for RAM video card or anything else.
If I were a smart shopper though I'd just wait for socket 1150 and haswell and still use my video card and RAM
I have a Q6600 PC (now relegated to running FreeNAS with a ZFS mirror for data storage).
the RAM is DDR2 (new RAM required)
the PSU is 4-5 yrs old and clogged with dust (new psu/fans)
the drives are spinning disks, and sata2
the video card is an 8800GTS
none of the components have warranty
no wireless N
if i play mix and match i need to deal with any potential driver/stability problems myself
I've done enough of that crap at work.
Cost-wise it is close enough that getting warranty, all new hardware and portability is worth it.
In my opinion.
Plus, when buying a new machine,
i still have the old hardware to re-purpose - like I did above, or on-sell / give away to someone else.
So i bought a macbook pro.
edit:
as to laptops being suitable for "real work" - well, depends on what you define as "real work".
My "real work" brings me in >100k / yr, so its real enough for me. I do network simulation, Windows SOE development, operating system/application compatibility testing, cisco switch/router/wireless AP console (which i can't do with a desktop computer AT ALL if the gear is in-situ) vSphere (Cisco UCS + Netapp Flexpod) cluster administration, etc.
A modern laptop handles all this just fine.
Yes, there will always be users who need desktop workstations. Just like there are those who need server clusters for R&D, etc.
the point is, for the VAST MAJORITY of users, laptops have become more than powerful enough, and have been for some time.
With regards to the mini - my mini was fine for desktop use. I was using for home-user day to day crap it in preference to the Core2 Q6600 before getting my MBP, due to preferring OS X.
They already are powerful enough for casual/home use - unless you're a gamer. And again, rather than upgrade it (which isn't really possible beyond RAM/disk), i've repurposed it - it now runs Lion Server as a toy/test box.