Agreed with the misconception issue on 4-strokes and weight. Usually, a 4-Stroke of similar output (60 2-Stroke -- 90 4-Stroke) are going to weigh about the same. 4-Strokes usually have a much smaller muffler than the 2-strokes. Some 2-Stroke mufflers are really heavy like Super Tigre. The issue with 4-strokes is more on height than anything else.

Comparision:

Tower .75
2.2 BHP at 15,600rpm
23oz w/muffler
3.6" length (backplate to drive washer)
1.63" width (exclude flanges)
4.0" height
$94.99

OS 91
1.6 BHP at 11,000rpm
24.2oz w/muffler
3.6" length (backplate to drive washer)
1.68" width (exclude flanges)
4.88" height
$279.99

2-Stroke advantages:
A little simpler though not much -- don't have to worry about valves or timing
More power for weight (but you have to be up in the RPM band)
Cheaper -- a lot

4-Stroke advantages:
Sounds sooooooo good.
More low end power and bigger props
Much more fuel effecient (over the life of the engine may even save hundreds of $$$ when you are paying $15/gallon)

Most my club are either/or types. We have about 100 members and its split about 60/40. The 60 -- 2-Stroke guys fly only 2-Strokes and the 40 -- 4-Stoke guys fly only 4s even in little planes. You'll get an all day argument if you between these groups if you ask which is better. My opinion is if its 90+ and you want it to sound good and spin a big prop then 4-Stroke it. If its really big go with gas. If its 60 or smaller and your looking to save money up front then 2-Stroke.