Google has announced a new file conversion feature in Google Docs that lets you convert files that are already uploaded to your document list into a Google Docs format, as opposed to only being able to do so upon upload.
For example, you can convert PDFs to text using Google's Optical Character Recogniton technology. Files that can be converted include:
For spreadsheets: .xls, .xlsx, .ods, .csv, .tsv, .txt, .tsb
For documents: .doc, .docx, .html, plain text (.txt), .rtf
For presentations: .ppt, .pps
For OCR: .jpg, .gif, .png, .pdf
To use the feature, simply right click on the file and click "make a Google Docs copy".