I've spent many hours with sketchup. I'm 34 years old and grew up with a computer in the house, so I imagine that helps.

My experience has been that it can be really frustrating to use at first. Youtube is a huge huge help. My advice for learning it is to watch a few beginners videos first, try to design something and let yourself get frustrated, then go back to youtube for some intermediate videos. Then play with it. You'll get over a hump and it will become second nature. Just plan to spend 10 hours or so messing with it before you get over that hump.

I use it for projects where precision is important. For example, when designing built-ins and kitchen cabinetry. So far I've built a few built-ins based on designs I did in sketchup. It really helped clarify things that would've otherwise required trial and error. I've also designed our kitchen, but I have yet to embark on that project.

I find sketchup less useful for pieces of free-standing furniture where the outer dimensions of the piece are more flexible. My approach to such pieces is to use pen and graph paper, and tweak dimensions as I build it. This also gives you the freedom to play with your design to work around your material (grain patterns, blemishes, etc). It's my personal view that working off of very precise plans actually makes woodworking less fun.

A middle ground is to do as Jim stated above- don't worry about planning your joinery in sketchup or doing exploded diagrams of every piece- just use it to mess with proportions. That makes a whole lot of sense to me.

To each his own, but it's very much worth giving it a good try and pushing through some of the frustrations to at least learn whether you enjoy it!