Ive got a TomTom and it has got its faults (shortest route) but I wouldn't be without it and everyone's got one because they are good. One thing I would avoid is the wife with an A to Z 
Agreed about the shortest route....but probably other makes do as well...it depends where the manu gets its mapping info from, i think tomtom buys it from Teleatlas.
Ive had 2 Tomtoms now.....the original tomtom go and now the 510....i like the wide screen on the 510...but my 510 has a screen fault on it....it flickers most of the time with a 'ghosting' effect.
Both the 510 and original Tomtom have weak screen mounts....ie after a short time the weight of the tomtom makes them 'droop' downwards.
The 510/710/910 does support RDS-TMC but with an external ariel but tomtom seems unable to produce one!! Ive had one on order since the beginning of June and tomtoms website has just changed the availability of the ariel from Q3 to Q4

Make sure you have the license number in the box and dont lose it!! (its comes preloaded so generally dont need it) as my orig tomtom wanted to have the licence number entered after an update once and it was missing from the packaging.....even tho i could produce proof of purchase tomtom support wanted £90 to issue another license number for it!
Advance planning on it is weak......once the route is planned as soon as you touch the screen to view the route for example it recalculates from where you are and not where you set the start address.
Thats the bad points......but i generally like it for ease of use, 3d map view, postcode entry (altho doesnt know all postcodes), ability to recalculate routes quickly and automatically if for example you choose not to turn where it says to.
Oh one other thing, it doesnt know bus stations! Try finding Birmingham bus station......its not sign posted until your within 100 yrds of it and can see it by then anyway!

And one more thing but about satnavs in general, i wouldnt buy one with a hard disk inside it......imo hard disks and vibration only lead to one thing
