keep the iMac , if you really need a portable then the question is for what you need it , the MacBookPro is alright if you dont have a iMac at home or if you need desperately all the processing power it offers which is less then a iMac has on offer , a good compromise would be to get a used MacBook in good condition if you dont need the processing power of the Pro , if you even need less then i would just get a msi wind u100 netbook and put snow leopard on it , works like any MacBook , i had one , sold it to a student who happened to be blind , as he did want "voice over" , because he said microsoft is charging £800 for a similar program to voice over , but voice over is free and included in every version of OSX , and a MacBook would be overkill already for most things he needs a portable for at university , and it serves him well , he was so happy about the little netbook and its performance with snow leopard and voice over that he bought himself a iMac for at home
so don't overestimate your needs on a laptop , and if you could be happy with a iPad screen size , but want more processing power and want something cheaper , a netbook is the ideal solution , at least if you choose a msi wind u100 or dell mini 10v as these are the 2 where its known to be nearly as easy to install snow leopard as it is on a MacBook , i mean the Blind student did buy my MSI wind and did the installing himself again as he did want to know how its done just in case , and he had no trouble whatsoever after i explained him that he need to swap the alt and windows key around in order to have alt and cmd at the same position as on a MacBook or Mac in general as it will make it easier for him to have all keys where they should be
the msi wind gets even recognized as MacBookPro by OSX 😀