The biggest downers for me in regards to A3000D are the lack of space in the case, and the very sensitive SCSI controller (kind of picky in regards to what else you've got installed in your system, and which devices you use in your scsi chain). Installation of accelerator cards with SCSI on them requires an INT2 patch. It's difficult to make use of your accelerator's SCSI activity led, since you need to patch up a wire that would somehow connect to the led adapter so that the accelerator SCSI chain activity signal would be received by the led adapter. Getting the SCSI controller updated to the latest revision of supported chips is tricky, as DMAC4 Ramsey7 and WDSCSI8 are kind of hard to find.
A3000 is great if you keep it nice and stock, e.g. 16MB fast ram, 2MB chip ram, 3.1 roms, and perhaps an A3640. Heavy expansion...nothing beats an A4000D or T. A3000T is a totally different story however.
The ultimate fun expansion Amiga system that is also quite capable is definitely the A1200. Parts for it are the cheapest of all Amigas and it's easy to relace a dead motherboard. :-)
