I had a TomTom Go 300 in my 182 (with a heat reflective screen) and it took ages to fix to a signal in the mornings and would not hold onto it. I tried moving it all over the windscreen without much success. Changed it for a Garmin Nuvi 300 and never looked back.
Either way, the new chipset SiRF III is more sensitive than the older one with faster TTF. It's like comparing a Pentium II to a Pentium IV.
The TomTom ONE or Garmin Nuvi 300 would be the way to go for anyone buying one now, which both have the new chipset. The TomTom software is better as it is more flexible in customisations: voices, alerts, etc. Sadly, I can't get Ozzy to tell me to "take the f*cking left turn" on my Garmin Nuvi 300!
KnightAzul