iPod Touch 3rd Generation, Battery Replacement Experience
The original battery would no longer hold a charge.
The most difficult part was removing the outer front glass. Luckily, I had purchased a small electronics repair kit awhile back and it had a plastic prying tool in it. The one provided with the battery replacement kit from iFixit was quickly mangled. Eventually I managed to pry the screen off, but damaged the rubber seal around the screen and the plastic outer frame. Surprisingly, everything still went back together fine, although there is a slight gap around the front glass now, but it's not terribly bad.
The iFixit guide for this procedure is actually pretty spot on. Certainly be extra careful when soldering the ribbon cable from the new battery. I used a small, low wattage (Weller BP865MP) battery operated soldering iron and it saved me from melting anything. My first attempt, one of the contacts came loose as I was fitting the battery back in, so I had to re-solder it. Definitely use some electrical tape to hold the ribbon cable down while soldering. I also used scissors to cut the old ribbon cable from the old battery, before I unsoldered and removed it. I had read that suggestion from another story here and it helped to prevent shorting anything out, in case the old battery had a residual charge.