Sharing stinks, but so do limitations
My girlfriend and I bought a 20" CD iMac as soon as they came out with the plan of adding my 20" dell monitor and sharing it as our main computer. We both have 'real' jobs, but I'm also a photographer, and she does studio art and graphic work for her job and for fun. The evening computer battle began almost immediately (we never actually fought, but at least once a week we both really want to do some work on the same night, so someone gets to wait). She usually wins because she bought the computer, I just own the second monitor. Anyway, eventually I revived my Pentium III college box, hooked it to another input on the dell monitor so one of us can at least browse or email while the other works on the iMac.
Originally we were going to get a mac laptop, use it with my 20" monitor, then eventually get a powermac, but then intel was announced and we decided an ibook would be a dumb investment.
Our current plan is to get a laptop of some sort for general use as well as some graphics work, then for me to get a mac pro (i can't accept the idea of an unupgradable computer, let alone one with a monitor stuck in it as well, i don't want to fool with a new purchase for another 4-5 years, and most importantly, i'll never be satisfied with an iMac because I'm stupid like that).
...might be genetic, my father couldn't satiate his lust for audio equipment until he owned all McIntosh (yes, the other 'Mac', extremely high end audio equipment, my father might pull in 45k a year but has a $10,000 amplifier and $3000 tuner in the living room). On a side note, we visited the McIntosh factory in Binghamton, NY a while back, and our tour guide was friends with Steve Jobs. he'd sold him plenty of McIntosh equipment, and even stayed at his house a few times.
anyway, my suggestion: Keep one of the laptops, even if just for browsing. Unless the wife rarely if ever uses the mac pro, it's still worth it. Having 2 computers has many advantages, plus you won't be getting all that much for an old powerbook anyway (the 12" still get more than they're worth though due to the lack of portable macbooks, but perhaps the wifey's laptop is worth less). With 2 computers you can search online to see what's wrong with the other, share files so you can view all your work from the couch if you're lazy or sick, and work simultaneously.
Finally, I'd give it a few months if possible. Waiting for leopard will save you $130, and who knows what'll happen with the 8-cores, perhaps even a slight price drop for the quads. Refurbished is probably the way to go for you as well, buy your ram elsewhere, the 7300 is probably fine for your non-video needs, plus you can upgrade it in the future to keep the machine up-to-date, and at least consider a dell 24", they're ugly but the screen quality is very good. An ad agency i worked for stopped buying 20" ACDs last year after trying a dell 24", they bought 40 mac pros and dell monitors while i was there, and they were huge aesthetic snobs. a new hire brought her dell laptop in to use for design work and they asked her to attach it to an ACD and keep it under her desk 'to keep up appearances'.
