As I mentioned above I have previously owned both the 45 and the 48 and love them. Garmin makes a great user interface and it is consistant from unit to unit. The 48 has been replaced by the GPS 76 and a more advanced GPSMAP 76. I own the latter. The 175 has been replaced by the 176. The GPS76, GPSMAP76, and GPS176 being all WAAS receivers. I have heard alot of banter as to why someone would ever need the accuracy of WAAS. I have been in plenty of places in the fog where being off in your position by a few hundred feet would make the difference between floating and going aground. For the $50 difference in price between the old 48 and the new 76, I would take the new product anyday. (As with all new technology, one never "needs" it until it has become well aceepted at which point we all think, how did we live without it.) In any case, I own the GPSMAP76 and have been very happy with it. It has a detailed basemap that includes roads, exit facilities, etc as well as the more germain coastal features and buoys. It includes all the features of the 48 and GPS76 along with the above. In addition, one has the ability to upload to the unit, from a CD, marina information, coastal detail, and spot soundings. Garmin is due to come out with a new series of CD''s called BlueChart which additional details this summer. Battery life is good, accuracy is unbelievable, its waterproof and it floats.
The GPSMAP 176, as I understand it, is a WAAS version of the 175 and takes chips that contain the mapping information. Garmin will be (or is) producing Bluechart chips for this product as well. Good luck.