jpg vs tiff

i have been working in jpg up untill this point, however the other day i went and talked to some one about cleaning up one of my pictures and he said to allways work in tiff, because every time you edit a jpg the quality is diminished and there is no way to get that back, so it sounds like i should be working in jpg, however i now have a few questions
should i convert from my raw images, or will it be ok to convert from the jpg, as long as i havent altered the photo?
and if this is true why doesnt my camera offer a tiff shooting mode?

oh ya, and should i use 16 or 8 bit for the tiff?

Yes, there are purists who decry the jpg format, saying that any loss ruins the print and that you should ONLY work in a lossless format. I agree, but not for those reasons. For me, when I am "working on" a shot, I will use the photoshop format to make temporary saves. Doing so allows me the ability save all my layers. Once I am happy with the results and call it "finished" I save it in jpg, highest quality.

But keep this in mind: A high quality (12 in photoshop) jpg save is very nearly lossless. You would have to open and resave literally hundreds of times to see any difference in the quality of the printed image. So even though, I am “finished”, I can still edit it again without any perceptible problem.

So, yes, I do "work" in a lossless format (photoshop) but that is the lowest reason on the totem pole – the real reason is to keep the layers.

Convert from RAW to TIFF. Some cameras do offer TIFF format but I wouldn't shoot in TIFF as those files will be much bigger than RAW.
16 bit TIFF offers more information than 8 bit. I think. This could probably be answered by someone more knowledgable.

I would convert from the raw file since that's the original. And you're right, when you shoot in raw, you get what you get. In jpeg, you get what you shoot after the computer in the camera tweaks it a bit. When I shoot stuff for the magazines I design, I always shoot in raw because I can do more with the image. Also, tiffs are good option for working with photos. They are "pure", more so than jpegs. So I would convert from raw to tiff.

I shoot in raw format and convert to 16-bit psd format. If you are editing jpegs, the edits should be done non destructively using layers. As you work, you can "Save As.." and choose tiff with no compression. Once you are satisfied with your editing, you can then save it as jpeg, and choose a compression of 10-12 without doing to much damage. As far as converting the mode from 8 bit depth to 16 bit depth and back again, I'm not sure what the advantages are, though perhaps someone else can point them out.

I've seen 30" X 40" prints made each time a HQ jpeg was rotated & then resaved. In the 6th print, I could see some artifacts, but I had to look hard for them. So, there is some room to play with. That being said, I would never do it 'cause a tiff gives me a comfort factor.
RSE is a great converter & I use it to make a lot of image corrections there before I ever get to PS.
For simple shots that are only cropped & sharpened in PS, I usually delete the tiff after 'cause RawShooter saves the changes made in conversion & I don't need to keep the 3X+ size of the tiff.
For instance, use the Snapshot feature & you can save several versions if you need a light & dark exposure for contrast control. The saved conversion info only takes up about 1KB of disk space.

I'll save complex tiffs with a lot of layers & selections too, but not often.
Generally I'll keep the web jpeg in the root folder to use as an index to what's in the raw files.
And that's just the advantages of using the free version.