Hi Air
Have a look at www.pocketgpsworld.com for general information about mobile navigation and TomTom. This is a UK-based site that focuses mostly on navigation solutions for PDAs (i.e. Windows Mobile and Palm machines), but there is some useful general information there too. You'll find information on lots of different software packages there too (Route 66 is one). Many of them will only run on Windows Mobile or Palm devices though, and will NOT work on any Symbian platform, much less S60 3rd Edition.
There are some FAQs at http://www.pocketgpsworld.com/modules.php?name=FAQ. You can also see reviews of various different Bluetooth GPS receivers on their site at http://www.pocketgpsworld.com/item-menu.php?idSubCat=5
TomTom is MUCH more intuitive to use than Nokia Maps (aka Smart2Go), but, as been mentioned by others, won't work with the internal GPS receiver. However, modern Bluetooth receivers are about the size of a box of matches, or there are some Bluetooth hands-free kits available which incorporate a GPS receiver too.
Of course, the basic Nokia Maps software is free, and you can buy a 7-day or 30-day navigation licence very cheaply to see if you like it. (Get the 30-day - it's only 20% more expensive and gives you more time to get used to it.) If you decide you like it, a 3-year navigation licence is only just over half the price of a copy of TomTom Navigator software only. For TomTom, you will have to add the cost of the GPS receiver to that.
There are two ways to buy TomTom Navigator. You can just buy the software, and buy the GPS receiver separately, or you can buy a bundle including the software and TomTom's own Bluetooth receiver together. (See http://www.tomtom.com/products/category.php?ID=2&Lid=1 for details of the various ways to buy it.) You do not have to use a TomTom GPS receiver - any Bluetooth one should work.
If you buy the TomTom software on a card, you will get a 512Mb miniSD card, and will have to transfer the files onto a microSD card before you put it into your N95. I would get the biggest microSD card you can (i.e. 4Gb for N95/E90 or 2Gb for other phones) so that you still have room for other files too. I installed TomTom on my E90, and had to temporarily clear some music files and photos off my 1Gb microSD to make room for it. I have a Windows PC and didn't buy the software on CD, so can't comment on installation from CD on a Mac.
Start with Nokia maps and see what you think. If you need something more intuitive, and arguably with better routing (I haven't compared them side-by-side), then TomTom's probably the way to go.
Julie