TempDB was where we first experimented with SSD's on our accounting system and it made a huge difference by greatly improving the I/O latency (we have a lot of EDI feeds into it). While I'd be first to say "write better code" it's usually not an option with most vendor's software so you opt for throwing more or better hardware at it, be it RAM or SSD's or some kind of indexing strategy. We will be spending a lot on SSD's this year where they will be dedicated to critical DBMS servers on our SAN, because like you said it can be a very cost effective tool.