I use gmail with no ill effects touch wood,i also filter my two old isp addresses through it.
The spam Filters are excellent and once you mark them as spam,they are automatically put in the spam box.
There is also a calender option,googledocs(excel,word type docs) and picasa that you can integrate into it.
In addition to above ive got 4GB of online storage space very useful if you want to upload stuff that you can access anywhere.
The search mail function is also very good,fast like googlesearch.
Also if you use gmail there is a addon "better gmail"
Which makes it customiseable.