Why are you still paying the airlines to ship your bags when FedEx Ground and other shippers will usually do it for less and with fewer hassles? Airline baggage fees (see chart) keep on going up, and while fewer bags are being lost (mainly because more people carry on these days), bags still get damaged, lost, stolen and delayed. Not only will it often cost less, but there are other advantages:

Better tracking: FedEx and UPS will allow you to track your shipment online.
Better reliability: FedEx and UPS have a better delivery record than the airlines
No waiting in line: no waiting to check your bags at the airport or to retrieve them at the carousel
Less theft: No light-fingered TSA agents or baggage handlers
Better insurance: airlines won't reimburse you for "valuables" (electronics, business effects, etc.) in your checked luggage in the case of damage or theft.  You can insure these with FedEx and UPS.
An apology if something goes wrong. And a refund: You'll get a refund of your shipping charges if the shipment is severely delayed or goes astray. Airlines only reimburse your bag fee if they lose your bag for good.
Even better than carryon: Sure, you can avoid some of these pitfalls by carrying on your bag, but then you have to fight for overhead bin space, if there's room in the overheads at all, in which case you have to check anyway.

Below, a couple of comparisons showing what you can save by shipping vs. schlepping. Note that since airlines charge the same fee for shorter flights as they do long ones, the savings are even greater for short-haul routes. And as soon as you go over the 50-pound weight limit, or over the typical 61 linear inch limit, where airlines really tack on the fees, the savings multiply.

I only show FedEx 5-day (or less) Ground rates here, assuming that you drop off the package at a local Kinko's or FedEx office. Home pick up will incur additional charges. UPS charges similar rates. All prices are one-way.

And yes, if you fly on Southwest you can usually avoid checked bag fees (under you're over 50 pounds), but all the other hassles of checked bags apply. Note, too, that if you're staying in one place when you arrive at your destination, you can save weight by just shipping the contents of your suitcase rather than the suitcase plus its contents. And while it's true that this method forces you to plan ahead, it's worth it: you'll save time and hassle--and probably money as well.

Route One: Boston to San Francisco

One 25-pound suitcase, under 61 linear inches

Delta (and other legacy carriers): $25
Fed Ex Ground 5-day service:  $34.44
Southwest: $0

Same route,  25-pound second bag under 61 linear inches

Delta etc.: $35 each way
Fed Ex Ground 5-day service: $34.44
Southwest: $0

Same route, but a 54-pound first bag, under 61 linear inches

Delta etc: $90-$100 overweight charge, plus $25 ($115-$125 total)
FedEx Ground: $61.53

Route Two: Los Angeles to Seattle

One 25-pound bag, under 61 linear inches

Delta (and other legacy carriers): $25 each way
Fed Ex Ground 5-day service:  $19.88
Southwest: $0

Same route, second 25-pound bag

Delta etc.: $35
Fed Ex Ground: $19.88
Southwest: $0

Same route, but a 54-pound first bag

Delta etc: $90-$100 overweight charge plus $25 ($115-$125 total)
FedEx Ground: $36.14
Southwest: $50