Good thinking. SOMETHING new is likely
And now is a good time to buy a G4 if now, not next year, is when you need a computer. Waiting makes sense otherwise--the G4 will be the first to go when the Intel transition begins. But now is a GREAT time to buy a G5.
There are indeed good reasons to choose to wait--Intel has some great chips planned. But there are also some VERY good reasons to choose to buy a Mac before the Intel transition:
1. ALL current apps will run great on PowerPC. No worries about what Rosetta will or will not run, and how fast. No worries about what is or is not optimized for the new platform. I suspect the non-Intel-compatible apps will be few--but there will be SOME at first, for the Intel Mac early adopters.
2. Most future apps too will run on PPC--and at full speed. Universal binaries. For years. Some won't eventually, but that's always the case with any computer purchase. Even OS X's next version, 10.5 Leopard, will run on PowerPC (which we know from the timing). And years from now, the one after that? Maybe.
3. You avoid the growing pains any new product line has. Let others--like me!--be the guinea pigs!
4. If you ever want to run Classic (OS 9) apps, you know you've got the option.
5. You get a new Mac NOW instead of in 6 months to 2+ years

Think what you could be doing with it...
6. And even if you switch to an Intel Mac later, you won't have to re-buy all your software. Most apps (anything G3-compatible) will run via Rosetta--and not half badly, from reports. Many apps will get free updates and run even better than that. But to be safe, If you plan to buy any big apps now, do ask the company if a free Intel Mac version will be made available--and if they can't answer, then wait a few months (for that app) until they can answer.
So buy now or buy later--whatever best meets your needs. Either choice has benefits. I know if I were still stuck on Windows, I'd want to get my computing life moved to Tiger ASAP

Preferably on a G5, but even a G4 Mini tempts me when I see them...
Don't mind the trolls, every forum has 'em