Helvetica

One more thing, this also completely obviates the need to worry about using expensive protease inhibitors or a range of different buffers (e.g. RIPA, NP-40, etc.) All cellular proteins are efficiently denatured, and even membrane-bound ones or extremely hydropho0bic ones end up in solution.

All the above are valid points if you are doing native western blots, but if you are running standard SDS-PAGE with denaturation and reduction of samples before loading, the best way to preserve protein integrity and to harvest total cellular protein is to lyse your tissue directly in 1X SDS-PAGE sample buffer, followed directly by heating at 70°C for 10 minutes. This irreversibly inactivates proteases, and results in complete destruction of all cellular membranes. After brief sonication to disrupt the DNA, you are left with a solution containing all cellular proteins as linear polypeptides which is stable at room temperature and can resist multiple freeze-thaw cycles.

The one disadvantage is that due to the presence of reducing agents in the sample (beta-mercaptoethanol or DTT), you must use a reducing-agent compatible assay for protein quantification. I prefer to use the Bio-Rad RC-DC kit (based ont he Lowry method) because it can tolerate relatively high concentrations of reducing agent. BCA-based assays (such as the Pierce BCA reducing agent compatible kit) are far too sensitive to reducing agent contamination to give reliable results.

A nice sample protocol for direct lysis of tissue is in this protocol published by Christer Ericsson and Monica Nistér (link is to a PDF):

http://www.biobanks.se/documents/Protein%20Extraction%2020030807.pdf

I would really urge everyone doing denaturing SDS-PAGE to use this protocol, it is by far the best way to minimize protein degradation and to extract total cellular protein.