IGN has been talking to Rockstar UK and got a most promising statement, considering that we’re talking about SecuROM: one time online authentication, unlimited installs on different machines:

“GTA IV PC uses SecuROM for protecting our EXE until street date has passed, to ensure the retail disk is in the computer drive, and is used for Product Activation of the title. Product Activation is a one time only online authentication when installing the game. GTA IV has no install limits for the retail disc version of the game, and that version can be installed on an unlimited number of PCs by the retail disk owner.”

Good news up till now. However, some players might not feel so good about the rest of the statement:

“You will only need to authenticate the retail disk once per Windows account per machine. Even if you uninstall and re-install the game, it will not have to be re-authenticated.”

In other words, something will remain installed on your machines, even though you managed to uninstall the game. It might be just a simple registry entry, but I wouldn’t bet on it, given the type of DRM used by GTA IV.