The latest bloviations by Gov. Rick Perry about secession may be gold ole' crowd-pleasing stuff, but there is the pesky matter of reality, which sooner or later intervenes when you think about this subject for more than about 90 seconds.
I tried discussing the idea of Texas secession with a secessionist about 10 years ago ago via email. It was a very frustrating conversation, because while he insisted that Texas had the right to secede, he could not point to any verbiage anywhere defining a process for secession from the Union. The U.S. Constitution lays down no process for secession. That's not to say it can't be done, but there is no Application To Secede that a state can fill out, take to Washington D.C. and get processed. The guy I was debating with claimed that Texas has the right to succeed under its accession agreement, but that agreement as far as I know says nothing about secession. After a while the debate fizzled out as I realized that we lived in different universes.
My understanding is that talk in the 1990's by the Partie Quebecois concerning secession for Quebec was stopped quite quickly when the President of Canada at the time, Brian Mulroney, informed the PQ that if Quebec wanted to secede, that they would also have to assume their pro rata share of the Canadian National Debt. That sort of reality check tends to quieten rooms in a hurry...
The bad news is that it doesn't matter whether you do it on population or land area, Texas will have a very large bill to pay if it wants to secede and carry a share of the US national debt. Of course, the secessionists will probably argue that they should not have to carry any of the debt because Those Nasty Other States ran up the tab...
The secession of Texas is likely going to result in a net fiscal loss for the USA, since the last available numbers from 2005 show that Texas is a net contributor to the Federal Government, taking $0.94 for every $1.00 it pays the Federal Government. However, a lot of military bases and locations in Texas will most probably be closed, or Texas will have to assume them and pay for them (this could mean goodbye to large sources of employment like Fort Hood, folks).
There will be other structural changes resulting from Texas leaving the Union. It is unclear to me how many creative and knowledge workers from the Austin and Dallas areas will stay. Many of them may move back to the rest of the USA, especially if the governance of the newly independent country of Texas is dominated by the sort of narrow-minded, mean-spirited, Christianist people that appear to be dominant in the current political processes and governance of Texas. This is a state whose Board of Education is currently converting itself to a laughing stock, there are massive issues with jurisprudence and the judicial system, and the state has trouble balancing its books every year, partly because there is no state income tax. Only tax havens tend to be able to avoid income taxes in the rest of the world, and I do not see Texas, which has a large land area which requires a lot of infrastructure to provision, can avoid The Subject That Must Not Be Mentioned if it tries to become an independent country. There is also the potentially crippling expense of border security. I haven't gotten out my ruler, but the length of the borders between Texas and the rest of the USA, plus the length of the border with Mexico, is going to add up to one hell of a border security challenge. As this official page shows, the length of the borders from the new country of Texas to the USA and Mexico is a sobering number (if you take the smaller published number) and a frightening number (if you go with the larger number).