I've been using Latex for several years, but recently I've found that I can get crazily varying compilation times.
For example: I am currently working on a ~15 page document with around 10 high quality eps/pdf figures and a bibtex bibliography. I find that for several days it will compile everything in ~30s. I then replace one word in the main body text, and compilation takes over an hour, with no new messages in the log. After another few days working on it, it goes back to 30s. This has happened previously as well with much smaller documents.
Clearing out auxiliary files has no effect on this: if it was compiling quickly it keeps compiling quickly; slowly then still slowly.
For reference I'm using pdfTeX 3.1415926-2.5-1.40.14 (TeX Live 2013) on Mac OSX 10.9.2. I've not included any sample code as this happens with such a huge range of documents and style files: I haven't been able to find a single culprit.
Has anyone seen or heard of anything like this before? I haven't been able to find anything online.
Edit: Thanks to @Heiko I've tracked the issue down to the float placement. However, I still don't know why this is such an issue. In particular, if I try to compile the document on a computer running Linux, the same document compiles in about 2s every time. So why are the floats causing such a problem on Max OSX?
microtypepackage: Disable microtype for a portion of a document. If you are using that, try taking that out and see if the compile time is improved.