The dictionary format has changed so dictionaries will need to be recompiled.
All data, by default, is now included in libdir/aspell-0.60 so that multiple versions of Aspell can more peacefully coexist. This included both the dictionaries and the language data files which were stored in sharedir/aspell before Aspell 0.60.
The format of the character data files has changed. The new character data files are installed with Aspell so you should not have to worry about it unless you made a custom one.
The dictionary option strip-accents has been removed. For this reason the old English dictionary (up to 0.51) will no longer work. A new English dictionary is now available which avoids using this option. In addition the ignore-accents option is currently unimplemented.
The flag -l is now a shortcut for --lang, instead of --list as it was with Aspell 0.50.
The Aspell 0.61 library is binary compatible with the Aspell 0.50 library. For this reason I chose not to increment the major version number (so-name) of the shared library by default which means programs that were compiled for Aspell 0.50 will also work for Aspell 0.61. However, this means that having both Aspell 0.50 and Aspell 0.61 installed at the same time can be pragmatic. If you wish to allow both Aspell 0.50 and 0.61 to be installed at the same time then you can use the configure option --incremented-soname which will increment so-name. You should only use this option if you know what you are doing. It is up to you to somehow ensure that both the Aspell 0.50 and 0.61 executables can coexist.
If after incrementing the so-name you wish to allow programs compiled for Aspell 0.50 to use Aspell 0.61 instead (thus implying that Aspell 0.50 is not installed) then you can use a special compatibility library which can be found in the lib5 directory. This directory will not be entered when building or installing Aspell so you must manually build and install this library. You should build it after the rest of Aspell is built. The order in which this library is installed, with relation to the rest of Aspell, is also important. If it is installed after the rest of Aspell then new programs will link to the old library (which will work for Aspell 0.50 or 0.61) when built, if installed before, new programs will link with the new library (Aspell 0.61 only).