Using an iMac G4 as your main computer depends pretty significantly on what you're using as your main computer right now.
If you're using a G3 as your main computer -- then sure, a G4 will be a big step up. If you're using anything x86 whatsoever, (even if that x86 machine is *also* from 2002/2003) then the G4 will be a step down. I've got a ThinkPad T30 from 2003 whose 1.8GHz Pentium 4 Mobile (Northwood, if I remember correctly) gets the same Cinebench results as the 2005 1.67GHz PowerBook G4.
So when it comes to Pentium 4s -- I wouldn't scoff too hard. Even if you're doing the same thing on it as you would be on a G4, it'll do them faster and you will be able to use newer software if you were so-inclined.
But it also depends on how old you are. Even though I had the TiBook, while I was in high school (2002-2006) my main computer alternated between an 840av and a bluewhite G3 -- just because I had nowhere near as much need to stay current with document formats or collaborate with anybody or use an email system with any modicum of security. (And most of the Internet email providers have ramped up the security methods they use on pop/IMAP connections since then anyway.)
As of today, a G4 can still do most of the Internet. (And it can run every program it could the day it was new, and other programs that'll run within what its got available.) And even more becomes technically (maybe not practically) possible if you're willing to run, say, "linux" on it. But leave it to the computer industry to invent a few more things in the next one to two years to make a G4 not very fun on the Internet.
If you're using a G3 as your main computer -- then sure, a G4 will be a big step up. If you're using anything x86 whatsoever, (even if that x86 machine is *also* from 2002/2003) then the G4 will be a step down. I've got a ThinkPad T30 from 2003 whose 1.8GHz Pentium 4 Mobile (Northwood, if I remember correctly) gets the same Cinebench results as the 2005 1.67GHz PowerBook G4.
So when it comes to Pentium 4s -- I wouldn't scoff too hard. Even if you're doing the same thing on it as you would be on a G4, it'll do them faster and you will be able to use newer software if you were so-inclined.
But it also depends on how old you are. Even though I had the TiBook, while I was in high school (2002-2006) my main computer alternated between an 840av and a bluewhite G3 -- just because I had nowhere near as much need to stay current with document formats or collaborate with anybody or use an email system with any modicum of security. (And most of the Internet email providers have ramped up the security methods they use on pop/IMAP connections since then anyway.)
As of today, a G4 can still do most of the Internet. (And it can run every program it could the day it was new, and other programs that'll run within what its got available.) And even more becomes technically (maybe not practically) possible if you're willing to run, say, "linux" on it. But leave it to the computer industry to invent a few more things in the next one to two years to make a G4 not very fun on the Internet.