If MacBooks are inherently slow when using Wi-Fi then there is something wrong with all of mine, because they run like blazes.
... I can see by the numerous posts and questions this is a very common issue that has been going on for years and the concerning thing is how many similar posts to mine don't seem to get resolved.
Your Mac obviously performed well when you bought it, or you would have either immediately returned it for a 100% refund or called AppleCare, who would have fixed it. If AppleCare is no longer an option for you then you have to provide specific details, ask others to help you, and then patiently wait for competent assistance. The only questions that remain unresolved are the ones that lack those requirements. There is an abundance of useful information on this site that will help, if you want to fix your problem and not just rant about it.
Specific guidance requires specific details - until you can provide them read the following:
OS X Mountain Lion: If your Mac runs slowly The article is very cursory, but be sure to read through to the end. Unfortunately the "Repair a disk" link at the end points to nothing useful, so use this one: Disk Utility.
General purpose Mac troubleshooting guide: Isolating issues in Mac OS X
Creating a temporary account to isolate user-specific problems: Isolating an issue by using another user account
Identifying resource hogs and other tips: Runaway applications can shorten battery runtime, affect performance, and increase heat and fan activity
To identify potential hardware problems: Apple Hardware Test
To resolve startup issues and perform disk maintenance, use Disk Utility.
Safe Mode or "Safe Boot" is a troubleshooting mode that bypasses all third party system extensions and loads only required system components. Read about it: Starting up in Safe Mode
To repair a potentially corrupt hard disk, so that you may recover its data prior to replacing it, and subsequently reinstall Mac OS X: OS X Recovery (applies only to Lion and later versions of OS X)
Both my 2010 and my 2013 (just transitioned and I still have the old one) run very well on wifi. The 2013 has the wifi issue everyone is talking about when I try to connect to the old Linksys router but it connects reliably to the Airport Extreme. In fact using 802.11AC the 2013 has a lightning fast connection.
I don't think the problem they are having now with the Haswell Macbook Airs (2013) is the same problem they have had previously. My 2010 NEVER had any problems. Annoying I know. Hopefully Apple will fix it soon.
The 2013 MBA is using a new WiFi standard and there are bound to be bumps in the road with new hardware. Many people are using their new notebooks without experiencing WiFi connection/speed problems but obviously some are. You can be sure that Apple wants to get this solved as badly as you do and Mac sites have reported that an update is in the works.
In the meantime you can do a little troubleshooting of your own. Go to the manufacturer's Web site and make sure your wifi base station is using the newest firmware. If you have a 802.11 ac station be aware that the standards have been in flux for a while (but apparently are close to being agreed to now) so there may be incompatibilities that will have to be fixed with a firmware update yet to come. Again, if you do have an AC base station if it can be configured not to use AC that may be a temporary fix.
So, I am a Mac fan for 30 years and have just about every device. No problems with any except within this year, my macbook air does not function well with wifi. It did when i first got it. I hadn't used it for awhile since I got my iPad...being obsessed with that. None of these explanations make any sense to me. You have a mac, it works. But not in this case. Can anyone just point to an update that fixes this. All of my other mac devices work fine....why not the macbook air?