I made the switch to Apple back when OSX first came out in BETA, ran it on a Strawberry iMac of the day. I've never regretted switching over.
I bought my 27" iMac January 2009, it is the 3.0Ghz Core-2-Duo model. It has worked flawlessly since new, as did the 20" iMac that I had for a couple of years. I use it for the usual internet things, plus I do music engraving with Finale and Sibelius as well as some other music related things. I've also done a couple of short videos with iMovie.
Performance on this one has been superb and I've never had it get sluggish over time. I am still running the same overall system I was the day I bought it with updates and upgrades to the OS as they have come along. IOW, this HD has never been reformatted, nor has the OS ever been reinstalled. Often, the OS upgrades/updates result in better performance.
Now to the price issue. Yep, you'll pay more for the Apple computers, but that is because Apple doesn't build to the lower end of the consumer market, that's a conscious choice by them. But one of the good parts is that when/if you decide to sell yours to get a new one, or a refurb, you can usually recover a significant % of the original cost. My 20" iMac sold locally for $800 after 2 years, I had paid about $1K as an Apple refurb when I bought it. That isn't uncommon at all.
One thing you might want to consider is where/how to buy one. If you look at Apple's online store, and scroll down to the lower left side, you'll see a link to 'special deals'. These are Apple certified refurbished models that carry the full Apple warranty and are eligible for Applecare (extended warranty) if you want it. If the model you are looking for is there, you can save a fair amount of money. I've bought almost all my Apple gear there, the 27" iMac was the exception as it was new to the market at the time. The only difference I have ever seen with the new vs refurb was that the refurb came in a plain box instead of the multi-color one. Well, that and saving a bunch of money!
I recently bought a MacBook Air there for $849. It is the current model that sells for $999 new. Can't tell the difference!
Here's the link to the 'special deal' on the 27" iMacs :
iMac 27" - Apple Store (U.S.)
Hope that helps.