Is there a limit (either recommended or forced) for mysql databases?

One of my db's sql dumps is now over 100Mb so I'm wondering if large databases have any negative effect on a sites performance? I haven't noticed any yet but would rather start planning something now if it's about to implode

100Mb may not even be that much but still better to ask just incase

The limitation is inherent to the system the DB engine run.
Or to be more precise, the file system format the DB datas files are placed.

The more common file systems and their max file size:
http://en.wikipedia.org/wiki/Exabyte

reiserfs 3/4: 8Tb
Ext2/3: 2 to 64 Tb
Xfs: 8 Exabytes (Holly smokes !!!!)

So, no, 100 Mb is not a so big DB in comparison.
I used to handle a DB that had reached 18 Go after 5 years (for a dating site).