Alright, I'm affraid your question is a touch too vague. "The MacBook" doesn't specify any particular laptop, MacBook refers to an entire line or family of products, also there is the "MacBook Air" which is the new Apple Ultra-Mobile.
As far as questions such as "is it worth it" I use the TCO to define wether a computer is worth it or not (Total Cost of Ownership).
To start, Mac's generally cost more for equivalent hardware than PCs. That is to say the raw specs, 4 Gig of RAM in a Mac cost more than 4 Gig for PC, a 3Ghz processor for Mac costs more than a 3Ghz processor for PC etc.
Apple's Mac OS also costs more, which isn't a big deal in the interim, but if you decide to keep Apple products into the next generation of Apple products it will cost a lot to upgrade to their next OS.
Programs generally cost 50% or greater more for the Mac OS than for other OSes, and Mac follows a very closed source mantra, which leaves little room for freeware/opensource projects to make programs for Mac.
Add on licensing fees, software upgrade fees etc. You can see how the Mac can be a very expensive system to own, Laptop or desktop.
So is it worth it? As far as hardware goes, no. It's trendy, and some people will spend extravagant amounts of money to be fashionable, ask a supermodel the same question.
The battery life of a MacBook is comparable to the battery-life of similar cell batteries on other Laptops, which generally means in the 2.5 to 3.5 hour range depending on usage. Though some of the laptops out there using new hardware technologies for low power consumption will last as much as 7hours of activity, such as the Via C-7 M processor.
What do you intend to use the Laptop for? Remember any software you already own for the PC will be obsolete, unless you plan on "dual booting" with windows, or running Windows in an emulated environment, at which point why spend the extra dough on a laptop to run windows that could have equivalent hardware bought cheaper from a different manufacturer?
Most games are released to PC first, some games never port to MAC and rely on emulators which do not perform as well as a native platform.
If you'd like to try breathing new life into your old laptop you might be interested in testing a Linux distrobution, these are generally free, and some such as Ubuntu will send you a CD or DVD copy of their OS distrobution for free.
There's still a lot of stigma around Linux, but there has been a huge movement towards usability. Many Linux releases now resemble or mimick better known Desktops such as Mac and Windows. If you're going to get an updated laptop anyway, it may be worth trying out Ubuntu or Dynebolic on your old Laptop.
P.S.
A Mac is not inherently more secure from viruses than a PC, it implements what's known as "Security by Obscurity" Which is to say it's a more obscure platform (Less users) so there's less reason to attack it.
A quick search online for Mac Viruses will turn up several hundred viruses that affect the Mac promptly. Don't be fooled. As with any Computer Operating System, exercise best practice. Know what you're downloading, installing, and where you're visiting.
I usually run on windows, have done so virus-free for over 5 years without employing any anti-virus protection on my computer. I do an occasional scan for posterities sake usually with online scanners, or with an AV program I have on my USB key.
P.P.S
The speed of accessing Wi-Fi and the Internet is not affected by the computer system itself, the speed of the internet it self is designated by the Internet Service Provider and maintained by the Access Point. (Router/DSL Gateway)
P.P.P.S
Buying a Mac is part of buying into a community, as stated before, it's a fashion statement. There is a mentality of superiority that most Mac users have. (I'm only mentioning this as I've already gotten a thumbsdown and my post is mere minutes old)
I've used Mac's, I've even been trained for Mac+ certification. They simply aren't all that Mr. Jobs would have his fans believe.
I've done video and graphic editing on PCs running Windows, Linux and on Macs, They used to have an edge, the Mac still does host some of the best (Read: Easiest to use) programs for video rendering.
That is about it.
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In response to RAM and Hard Drive upgrades on other Laptops, Hard-Drives are usually as easy as sliding one out and a new on in on most Laptops, RAM usually has one screw securing it's cover, remove the Screw and the RAM is extremely easy to remove and add new and properly seat. I hear more horror stories of RAM becoming improperly seated in Macs than in any PC, and it's not any more difficult in a PC, and as stated before, generally much cheaper for the PC.