geth saves its internal states for the main network in the chaindata directory. You can find it in the directory:

• ~/.ethereum on linux
• ~/Library/Ethereum on OS X
• ~/AppData/Roaming/Ethereum

It uses the LevelDB database. You can save this directory only if geth is stopped to prevent corruptions. The data is portable on Linux, Windows and MacOS X (i have checked). But you have to remember that it is not a safe way. Do not use a chaindata archives provided by anonymous. The transactions are not checked! When geth starts, it checks all the files are present. If a .ldb file misses, the chaindata directory is corrupted and you have to remove this directory!

geth import and export is safe but slow because all transactions are checked and the operation is the same as geth without the --fast flag. On my 3720qm, it is 5h and 19Go disk storage used. The only economy is the network download (1.5Go). It is faster to do a geth --fast!

On my intel 3720qm mac mini (1Gbit/s), some benchs geth 1.4:

__________________________________________________
| Operation   | Disk Used | Time | Disk Written  |
|-------------|-----------|------|---------------|
| geth        | 19.Go     | 5h00 | 1To           |
| geth import | 19.Go     | 4h50 | 1To           |
| geth --fast | 3.7Go     | 1h00 | 100Go         |
--------------------------------------------------

On my intel 3720qm mac mini (1Gbit/s), some benchs geth 1.5 (in dev):

__________________________________________________
| Operation   | Disk Used | Time | Disk Written  |
|-------------|-----------|------|---------------|
| geth --fast | 3.8Go     | 17m  | 25Go          |
| geth        | 19Go      | 2h   | 100Go         |
--------------------------------------------------

Conclusion:

• i uses chaindata archives only between my computers.
• import is very slow, check all and saves all states.
• geth --fast is faster and saves only current states.