Thank you all for the support,
I guess there are two problems for me to move from Picasa to other software (like Aperture, Lightroom, iPhoto)
- I have my 2,000+ photos tagged in Picasa which I think none can import. If I have to do it all again, it will be too much work
- Picasa is Free compared to other softwares and is available in mac version.
So thanks for the support and I know that I can always rely on this website and its strong support of pro members for help.
If you know of any software that can turn Picasa tags into generic tags that can be used for any software like (Aperture, Lightroom, iPhoto) please let me know.
Till that time my workflow will be as follows
1. Shoot in RAW
2. Download using DPP (I have Canon EOS 450D)
3. Correct White Balance in DPP
4. Correct Exposure in DPP
5. Export it in jpg
6. Edit it in Gimp (If I need to)
7. To send it to friends, resize it and then make a Picasa album to share
Well I guess, Mac or Windows does not matter in this case.