I know the 3rd edition - it was the book my sophomore "probability for engineers" course was based on. At the time I thought it was a good book, with plenty of theory and lots of examples so the reader could pick and chose which ones were helpful. I'm sure we skipped the more difficult proofs, and I'm sure we didn't do the hardest problems in the book, but I know that I gained a working knowledge of probability. Years later I used this book as the first part of my "probability review" I undertook on my own once I was in the workforce and needed better fluency with the material, and I thought Ross was great as far as basic probability is concerned.
Are there better books around? Probably. But Ross is reasonable. Now there is a 9th edition out, which (surprisingly) only about 15% longer, so hasn't suffered the extreme bloating many books have. The price of the new edition is outrageous, though. The book is not worth $145 in my opinion, no matter how much better it is than he 3rd edition.
jason