GeoTiff size limit - and other raster files

[pitzoni]

Hi all,

I'm looking for a raster format that can store DEM/DTM data in 16/32bit (no text formats). So:
1. Is it true that the Tiff/GeoTiff format has a file size limit of 4GB - or is this an historic fact?
2. Is there a raster format where I can alter the tiling size within a single file? My intention is to store in a single file few areas where each has a different resolution?
3. My intention is to use mostly GIS-and-Photogrammetric related softwares. Is ERDAS's IMG file format is an alternative? Any other file formats out there?

Thanks,
Pitzni